[MERGE] 3-number dotted revnos

[Ian Clatworthy]

John Arbash Meinel wrote:
> Attached is my dotted revno update. I also included a bit of user guide
> documentaition, but I didn't know where to "include" it.

bb:tweak

I really like this. Long (and growing) revision number sequences have
been a UI wart of ours that I'll be pleased to see go. Thanks for the
emails to the list outlining the various options you considered as well.
I think you picked the right one BTW. Some requested tweaks below.

Documentation. The new text is pretty good though the first 2 paragraphs
 should go given they effectively repeat the text from "Core concepts"
in the User Guide. As suggested by Eric, the new text should go in the
"Getting started" chapter immediately after the "Entering commands"
section. I'd like the section to be titled "Understanding revision
numbers" and for a cross reference out of "Revisions" in "Core concepts"
to it. Perhaps a cross-reference from when log is introduced would be
nice as well. (I'm happy to add that later though when I next polish the
UG to reflect the post 1.0 improvements.)

Code. This looks good except you forgot to update the docstring for
MergeSorter.__init__(). The "..." bit can go now that revision numbers
have either 1 or 3 parts only.

Tests. The only bit I don't understand is how the "merge depth" is
calculated by MergeSorter. In particular, in test_merge_sort_race, why
is the merge depth of C 1 (and not 2)? (Might be best to explain this
over IRC or phone as it's probably a bug in my brain.) Otherwise, all
the new tests and changes look good to me.

Ian C.