Cleaned up fgOpenWindow():

Cleaned up fgOpenWindow():
 * Removed TABs.
 * Made indentation consistant.
 * Deleted say-nothing-new comments.
 * Changed an *error*check* from an assert to an if().
   (The error-check was on window creation; we don't want to
    lose that if the user compiles with asserts deactivated.
    Also, assert()s really tell us more about programming errors,
    rather than run-time errors, so it is a little misleading to
    use assert() for error-checks, even if you can depend upon
    assert()s never being compiled away to null statements.)
 * Added some XXX comments for things that bear some rumination.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@275 7f0cb862-5218-0410-a997-914c9d46530a