Use XParseGeometry for better geometry parsing.

Use XParseGeometry for better geometry parsing.
Moved geometry parsing to after fgInitialize() so we can use the screen size
to correctly calculate negative positions in the geometry string.
Copied the code for XParseGeometry from the X11 sources for use in the
Win32 version.
freeglut now passes test1 of the glut test suite.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@355 7f0cb862-5218-0410-a997-914c9d46530a