Remove deprecation warning on OS X 10.9

GetCurrentProcess() is deprecated on 10.9.
So make a universal solution by checking OS version number.
get_system_version() function is the recommended Apple way of getting the OS version, since Gestalt is also deprecated (and does pretty much the same thing anyway)

Updating HIDRemote.m to use a similar function would allow to get rid of the 2 other warnings.