Add cputest for rlwimi/rlwinm/rlwnm.
These instructions are a bit mind bending.
Merge pull request #14 from Sonicadvance1/rlw_unittests

Add cputest for rlwimi/rlwinm/rlwnm.
Add test case for segment register setting/getting.

This adds tests for mtsr, mfsr, mtsrin, and mfsrin.