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Add back the Doom PWAD reload hack.

This was removed back in d190b596c566394717324296cbf6b46e67c64f5c;
at the time I didn't understand what it was or how it was supposed
to be used - it seemed like cruft left over from Doom's development.

It is actually a potentially useful feature for level authors when
developing their maps. See here: http://doomwiki.org/wiki/Reload_hack

The reload hack is a relatively obscure feature of limited usefulness
nowadays, but nonetheless a technical curiosity that ought to be
preserved in Chocolate Doom.

The reimplementation here is a lot cleaner than the original version
from the source release: W_Reload() is based on a call to W_AddFile(),
we don't reopen the reload file every time we want to read a lump,
and we include a check in W_AddFile() that we are not trying to use
the hack on more than one PWAD file.

This fixes #539.

--- a/src/doom/p_setup.c

+++ b/src/doom/p_setup.c

@@ -770,7 +770,10 @@

     // UNUSED W_Profile ();

     P_InitThinkers ();

-	   

+

+    // if working with a devlopment map, reload it

+    W_Reload ();

+

     // find map name

     if ( gamemode == commercial)

     {

--- a/src/strife/p_setup.c

+++ b/src/strife/p_setup.c

@@ -785,6 +785,9 @@

     // UNUSED W_Profile ();

     P_InitThinkers ();

+    // if working with a devlopment map, reload it

+    W_Reload();

+

     // [STRIFE] Removed ExMy map support

     if (map<10)

         DEH_snprintf(lumpname, 9, "map0%i", map);

--- a/src/w_wad.c

+++ b/src/w_wad.c

@@ -39,7 +39,7 @@

 typedef struct

 {

     // Should be "IWAD" or "PWAD".

-    char		identification[4];		

+    char		identification[4];

     int			numlumps;

     int			infotableofs;

 } PACKEDATTR wadinfo_t;

@@ -57,16 +57,20 @@

 //

 // Location of each lump on disk.

-

-lumpinfo_t *lumpinfo;		

+lumpinfo_t *lumpinfo;

 unsigned int numlumps = 0;

 // Hash table for fast lookups

-

 static lumpinfo_t **lumphash;

-// Hash function used for lump names.

+// Variables for the reload hack: filename of the PWAD to reload, and the

+// lumps from WADs before the reload file, so we can resent numlumps and

+// load the file again.

+static wad_file_t *reloadhandle = NULL;

+static char *reloadname = NULL;

+static int reloadlump = -1;

+// Hash function used for lump names.

 unsigned int W_LumpNameHash(const char *s)

 {

     // This is the djb2 string hash function, modded to work on strings

@@ -148,8 +152,26 @@

     filelump_t *filerover;

     int newnumlumps;

-    // open the file and add to directory

+    // If the filename begins with a ~, it indicates that we should use the

+    // reload hack.

+    if (filename[0] == '~')

+    {

+        if (reloadname != NULL)

+        {

+            I_Error("Prefixing a WAD filename with '~' indicates that the "

+                    "WAD should be reloaded\n"

+                    "on each level restart, for use by level authors for "

+                    "rapid development. You\n"

+                    "can only reload one WAD file, and it must be the last "

+                    "file in the -file list.");

+        }

+        reloadname = strdup(filename);

+        reloadlump = numlumps;

+        ++filename;

+    }

+

+    // Open the file and add to directory

     wad_file = W_OpenFile(filename);

     if (wad_file == NULL)

@@ -158,6 +180,13 @@

 	return NULL;

     }

+    // If this is the reload file, we need to save the file handle so that we

+    // can close it later on when we do a reload.

+    if (reloadname)

+    {

+        reloadhandle = wad_file;

+    }

+

     newnumlumps = numlumps;

     if (strcasecmp(filename+strlen(filename)-3 , "wad" ) )

@@ -539,8 +568,7 @@

 {

     unsigned int i;

-    // Free the old hash table, if there is one

-

+    // Free the old hash table, if there is one:

     if (lumphash != NULL)

     {

         Z_Free(lumphash);

@@ -566,6 +594,49 @@

     }

     // All done!

+}

+

+// The Doom reload hack. The idea here is that if you give a WAD file to -file

+// prefixed with the ~ hack, that WAD file will be reloaded each time a new

+// level is loaded. This lets you use a level editor in parallel and make

+// incremental changes to the level you're working on without having to restart

+// the game after every change.

+// But: the reload feature is a fragile hack...

+void W_Reload(void)

+{

+    char *filename;

+    int i;

+

+    if (reloadname == NULL)

+    {

+        return;

+    }

+

+    // We must release any lumps being held in the PWAD we're about to reload:

+    for (i = reloadlump; i < numlumps; ++i)

+    {

+        if (lumpinfo[i].cache != NULL)

+        {

+            W_ReleaseLumpNum(i);

+        }

+    }

+

+    // Reset numlumps to remove the reload WAD file:

+    numlumps = reloadlump;

+

+    // Now reload the WAD file.

+    filename = reloadname;

+

+    W_CloseFile(reloadhandle);

+    reloadname = NULL;

+    reloadlump = -1;

+    reloadhandle = NULL;

+    W_AddFile(filename);

+    free(filename);

+

+    // The WAD directory has changed, so we have to regenerate the

+    // fast lookup hashtable:

+    W_GenerateHashTable();

 }

 // Lump names that are unique to particular game types. This lets us check

--- a/src/w_wad.h

+++ b/src/w_wad.h

@@ -56,6 +56,7 @@

 extern unsigned int numlumps;

 wad_file_t *W_AddFile (char *filename);

+void    W_Reload (void);

 int	W_CheckNumForName (char* name);

 int	W_GetNumForName (char* name);