workaround absent CLOCK_MONOTONIC on OSX

Your vendor has not defined Time::HiRes macro CLOCK_MONOTONIC, used at ../lib/IPC/Cmd.pm line 767.

http://www.cpantesters.org/cpan/report/b6e98b7a-2a68-11e3-b2ac-8f6380b60443
typo
removed unused code
commented a bit
Merge pull request #9 from kohts/master

workaround absent Time::HiRes::CLOCK_MONOTONIC on OSX