macosx_application: remove deprecation warning on OS X 10.9

GetCurrentProcess() is deprecated on 10.9. 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.