Switch from libglut to freeglut and retire libglut. Libglut hasn't been 
developed in years and has been dropped from the MESA 8.0 distribution. 
Freeglut is a rewrite of glut and is actively developed and is used by 
many linux distributions instead of libglut. 

Because freeglut doesn't have de same dependancies as libglut, some ports need
extra dependencies added to USE_GL and USE_XORG to make them build.

Mark graphics/f90gl broken, f90gl depends on a header that is only shipped
	with libglut.
Remove option for libglut/freeglut selection in games/cake, only freeglut
	remains now.
Fix a png related build issue games/vegastrike while here.

Bump all ports that directly depend on libglut because of the shlib bump.

Collaboration with:	Niclas Zeising <zeising@daemonic.se>
Obtained from:	xorg-dev staging area.