A few big changes in this commit:

A few big changes in this commit:

1. The current indexer has been moved to backends/indexer_dbm in
   anticipation of my writing an indexer_rdbms,
2. Changed indexer invocation during create / set to follow the pattern
   set by the metakit backend, which was much cleaner, and
3. The "content" property of FileClass is now mutable in all but the
   metakit backend.

Metakit needs to be changed to support the editing of "content". Hey, and
I learnt today that the metakit backend implements its own indexer. How
about that... :)

git-svn-id: http://svn.roundup-tracker.org/svnroot/roundup/trunk@2157 57a73879-2fb5-44c3-a270-3262357dd7e2