This speeds up the in-memory version of debugbuilddag that I'm
working on considerably for the case where we want to build just
a 00changelog.i (for discovery tests, for instance).
There are a couple of test changes because node ids in tests
have changed.
The changes to the patch names in test-mq-qdelete.t were required
because they could collide with nodeid abbreviations and newly
actually do (patch "c" collides with id "cafe..." for patch "b").
When issuing `hg pull -r REV` in a repo with no common ancestor with the
remote repo, the message 'requesting all changes' is printed, even though only
the changese that are ancestors of REV are actually requested. This can be
confusing for users (see
http://www.selenic.com/pipermail/mercurial/2010-October/035508.html).
This silences the message if (and only if) the '-r' option was passed.
