* Updated to ZDoom r4318:
- Added more string functions to ACS: strcmp, stricmp (aka strcasecmp), strleft, strright, and strmid.
- Clean up excess code around a few calls to SingleActorFromTID(), since that function is already designed specifically to handle the case where tid is 0.
- Added GetActorClass and GetWeapon functions to ACS.
- Added S_ChangeSoundVolume() to change the volume of an already playing sound, accessible through the new ACS function SoundVolume.

git-svn-id: http://mancubus.net/svn/hosted/gzdoom/trunk@1587 b0f79afe-0144-0410-b225-9a4edf0717df