[MERGE] Remove specialized has_revisions() implementation.

[John Arbash Meinel]

John Arbash Meinel has voted approve.
Status is now: Approved
Comment:
I was a bit concerned, as I hadn't seen those changes, but it seems 
Robert sneaked in a couple of "trivial" patches without announcing them 
on bazaar at .

Anyway, seems fine, and shouldn't be introducing a lot of overhead. (I'm 
pretty sure doing _iter_entries() directly will be slightly better, but 
probably not enough to worry about yet.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20080704102033.GA6163%40vernstok.nl%3E