Add extra GE_TEXFUNC_UNKNOWN1/2/3 which handle same as GE_TEXFUNC_ADD
enum for GE_TEXFUNC_UNKNOWN1/2/3 = 5/6/7
Merge pull request #4821 from raven02/patch-8

Add extra GE_TEXFUNC_UNKNOWN1/2/3 which handle same as GE_TEXFUNC_ADD