move GL extensions into glexts.h

git-svn-id: svn://svn.code.sf.net/p/sauerbraten/code/src@5043 07af1644-1164-4067-b897-63bf4dc9b748

Conflicts:
	rpggame/Makefile
	rpggame/rpg.vcproj
	xcode/sauerbraten.xcodeproj/project.pbxproj
add glexts.h to VC filters

git-svn-id: svn://svn.code.sf.net/p/sauerbraten/code/src@5044 07af1644-1164-4067-b897-63bf4dc9b748
Better diff.