Fix broken mlock call

Should be a MlockRaw, not an Mlock. Got broken in the transition to Base::Mlock.
Add missing exception
posix_malign returns non-zero on error

The return code is likely positive to indicate the error code.
Lower the ram requirements of index_manager.test
Merge pull request #45 from cmaloney/mlock_fixes

Misc Fixes around the Mlock pull request