[MERGE] intern() various file_id/revision_id

[Martin Pool]

Martin Pool has voted resubmit.
Status is now: Resubmit
Comment:
Basically every time I've tried string interning in Python it's been a 
disappointment, even in cases where it would very likely have helped to 
do the equivalent in Java or Lisp.  So I'm skeptical of merging this 
unless you have at least ad hoc measurements that it does help.

I think you have to get a pretty high hit rate to overcome the 
apparently high overhead of interning them.

I'm going to mark it resubmit to get it off my queue, but you can merge 
if you find it's useful.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C49ADFD32.2070408%40arbash-meinel.com%3E
Project: Bazaar