Cleaned up status and filter filename and string handling.

The changes make git's status and diff match my workflow. In
particular, git status/diff should:

  * say there are diffs when I haven't yet expanded a media file;

  * not say there are diffs when my expanded media are unchanged;

  * say there are diffs when my expanded media are changed;

  * work on windows (git bash) and on linux (bash).
Version to 0.1.2.cb.1, update README, update packaging (don't know ruby...).