WIP Chromite supporting "LEGACY" mode, as requested by Anush.

WIP Chromite supporting "LEGACY" mode, as requested by Anush. 

This version of chromite supports the following features: 
1. Can be run from inside or outside the chroot. 
2. CWD can be anything when chromite is run. 
3. Current commands are build, clean, distclean, ebuild, 
emerge, equery, portageq, shell, workon. 
4. Build spec files can be named on command line using any 
substring. 
5. Build commands can be named on command line using any 
prefix. 
6. Menu driven for easy discovery. 
7. Chroot specs can be specified for any command with --chroot, 
which must be the first thing on the command line (so it's 
not interpreted as the arg to sub commands). By default, the 
'chroot.spec' is used. 


See http://codereview.chromium.org/6005004 for history.  
This is a separate CL, since Anush has requested this be
checked into the new 'chromite' repo.  This CL has the minor
change that a few paths are adapted to chromite's new location.

Future checkins will:
- Add wrapper scripts for inside and outside the chroot so
  that we can put chromite in the path
- Add more unit tests
- Address some of the TODOs in the file.

BUG=chromium-os:10556
TEST=Ran chromite_unittest.py; played w/ various commands.

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=f0c7395

[diandersAtChromium, 2011-01-18 21:45:33]

I will be committing this based on LGTM and reviews in:
  http://codereview.chromium.org/6005004