added hard check for python version, supporting only version 2.7+
improved OS version checking
added 'WARN' logging level (used in cases such as warning about unsupported OS versions)
fixed bug in overRide plugin, where if an exception was thrown (e.g. file-not-found), other items would be skipped
setup '-timeout' flag for system_profiler only when the OS supports it (e.g 10.9+)
added extension.Extension to custom json encoder (fixes issue: #15)