ui: store pushloc as separate attribute The magic @property is going to interfere with the ability to print path sub-options. We only access it in one location and it is trivial to in-line, so do that.

commands: add debugdeltachain command We have debug commands for displaying overall revlog statistics (debugrevlog) and for dumping a revlog index (debugindex). As part of investigating various aspects of revlog behavior and performance, I found it important to have an understanding of how revlog delta chains behave in practice. This patch implements a "debugdeltachain" command. For each revision in a revlog, it dumps information about the delta chain. Which delta chain it is part of, length of the delta chain, distance since base revision, info about base revision, size of the delta chain, etc. The generic formatting facility is used, which means we can templatize output and get machine readable output like JSON. This command has already uncovered some weird history in mozilla-central I didn't know about. So I think it's valuable.

histedit: pick an appropriate base changeset by default (BC) Previously, `hg histedit` required a revision argument specifying which revision to use as the base for the current histedit operation. There was an undocumented and experimental "histedit.defaultrev" option that supported defining a single revision to be used if no argument is passed. Mercurial knows what changesets can be edited. And in most scenarios, people want to edit this history of everything on the current head that is rewritable. Making histedit do this by default and not require an explicit argument or additional configuration is a major usability win and will enable more people to use histedit. This patch changes the behavior of the experimental and undocumented "histedit.defaultrev" config option to select an appropriate base revision by default. Comprehensive tests exercising the edge cases in the new, somewhat complicated default revset have been added. Surprisingly, no tests broke. I guess we were never testing the behavior with no ANCESTOR argument (it used to fail with "abort: histedit requires exactly one ancestor revision"). The new behavior is much more user friendly. The functionality for choosing the default base revision has been moved to destutil.py, where it can easily be modified by extensions.