Use vm_stat command on darwin to get memory

This has the benefit of allowing us to also grab the cached memory so
that we can get an "available" measurement

process[linux, darwin]: implements Connections using lsof.

Support 32-bit linux, this field is int32 on 32-bit systems

Add process/Parent, net/NetConnections on darwin and linux

Add common.invoker interface to mock exec.Command. common.FakeInvoker returns
expected file if exists instead of invoke exec.Command.
Currenly, mocking is enabled only process.Pids(). I will expand to other funcs incrementally.

Detect error in CPUTimes fails on callPs, and modify comments on ReadLines

Ensure that process.MemoryInfo returns a up-to-date value.

Fix net stat reporting for Darwin

DiskPartitions Fails if cd not in drive And used and usedPercent are missing in windows

Fix cpu percent on windows

Tested on windows 7:

When divided by 100 you get cpu percentage of  %0.14 when task manager shows %14. Once this is removed they match.

add used and usedPercent back in

Fix windows compile issues