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
Joystick fixes/update for non-MSVC compilers

* This fixes building on non-MSVC compilers for Windows since they don't
know `_tcsnlen()`.
* Changed logic so SFML tries to retrieve the paths from the user key
first, machine key second (typical behavior for most registry settings).
* Removed the registry key length checks since that check is performed
inside`RegOpenKeyEx()` anyway and cut-off keys might point to the wrong
keys.
* Updated the error string retrieval to properly handle errors.
Fixed font glyphs always being 2 pixels larger than they are supposed to be in each dimension, fixed wrong underline offset with some fonts, offset underline and strike through by half of their thickness so their center is positioned correctly, changed glyph and font metrics to use floats instead of ints to support scaling better.