Rewritten SVQC stringbuffer saving routines (which is part of yet unfinished databuff...

Rewritten SVQC stringbuffer saving routines (which is part of yet unfinished databuffers extension). Changes are backwards compatible with old savefile format. Now, once saved stringbuffers are found in extended savegame section, all string buffers allocated by worldspawn()/entityspawn (which is processed prior to savegame parsing) are deleted, and stringbuffers are restored from savegamefile with their original handles.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11930 d7cf8633-e32d-0410-b094-e92efae38249