[MERGE] annotate on working tree with edits

[Ian Clatworthy]

As Aaron and I discussed on the list a few days ago ...

>> The annotate
>> > command however ignores this capability and always annotates a
committed
>> > revision tree - the last committed one by default. Is that a historical
>> > thing or something we want by design?
>
> Historical accident.  When I added that capability, other people were
> actively working on the commandline annotate.  I didn't want to
> introduce conflicts, so I left it to them.  I just implemented it for
> gannotate.  They never saw fit to implement it for the commandline
> annotate, and I don't really care about it.

The attached patch addresses this. The changes are effectively these:

1. annotate_file can now optionally annotate a tree, not just a branch.
2. cmd_annotate in builtins.py now uses this capability.
3. Tests added.

In particular, the code in cmd_annotate has been refactored to look a
lot like the code in gannotate.

BTW, Aaron also requested some other changes to annotate. I'll tackle
those after this one has landed (or been rejected).

Ian C.