joystick:
- only poll joysticks if we have an active joystick
- active joystick is defined as having callback and having positive (NON-ZERO!) pollInterval, as per GLUT sources
- use fgState.NumActiveJoysticks instead of fghHaveJoystick to save bunch of unnecessary function calls etc
- fghcbCheckJoystickPolls more concervative, per window we first check if a joystick is active (per above definition)
git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1554
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