This adds the long-awaited indexfile feature, so you no longer have to feed

your backups through tar.

Okay, 'bup save' is still a bit weak... but it could be much worse.

Merge branch 'indexfile'

* indexfile:
  Minor fix for python 2.4.4 compatibility.
  cmd-save: completely reimplement using the indexfile.
  Moved some reusable index-handling code from cmd-index.py to index.py.
  A bunch of wvtests for the 'bup index' command.
  Start using wvtest.sh for shell-based tests in test-sh.
  cmd-index: default indexfile path is ~/.bup/bupindex, not $PWD/index
  cmd-index: skip merging the index if nothing was written to the new one.
  cmd-index: only update if -u is given; print only given file/dirnames.
  cmd-index: correct reporting of deleted vs. added vs. modified status.
  Generalize the multi-index-walking code.
  cmd-index: indexfiles should start with a well-known header.
  cmd-index: eliminate redundant paths from index update command.
  cmd-index: some handy options.
  index: add --xdev (--one-file-system) option.
  Fix some bugs with indexing '/'
  cmd-index: basic index reader/writer/merger.