Rearrange some things.

This splits DexOptimize into DexPrepare (which deals with file shuffling
and fork/exec) and Optimize (which does the actual quickening of
instructions).  The Optimize functions are now effectively private to
the "analysis" directory.

Twiddled some comments.

No substantive code changes.

Change-Id: Ia51865b259fb32822132e2373997866e360ca86a
10 files changed