Fixed memory leak in Unix JoystickImpl, refactored joystick code for all platforms, prevent accelerometers registering as joysticks on Unix.
Amended based on comments from last commit.
Added support for OS X 10.10

Note: this only fix the compilation process. SFML was not thoroughly
tested on this OS yet.
Merge branch 'bugfix/joystick'
Updated OS X Pool Wrapper
Fixed trying to truncate registry key names that did not need truncating. (#701)
Improved cursor hiding on OS X