All doubles now GLdoubles (important for GLES later)

All doubles now GLdoubles (important for GLES later)
Other general cleanup in prep for porting geometry code involving
circles.
no longer computing a larger circle table when only need half of it

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1192 7f0cb862-5218-0410-a997-914c9d46530a