Use snprintf or _snprintf instead of the potentially dangerous sprintf

Use snprintf or _snprintf instead of the potentially dangerous sprintf
to avoid warnings.

NOTE: Due to excessive use of #ifdefs, the joystick code is on the
border of being unmaintainable! I could only check that it compiles
cleanly on my Linux box. Others should test this on their platforms
(Windows, Mac OS X, *BSD) to make sure that nothing has been broken.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@784 7f0cb862-5218-0410-a997-914c9d46530a