docs: import figure diagrams with inkscape 0.92 No changes to the content here. This simply accepts the default option ("This file contains digital artwork for screen display") on the prompt when first opened, which is trying to upgrade from 90DPI to 96DPI.

messages: standardize on "working copy is now at" including "is" It seemed that we mostly used "is", but `hg next` and `hg prune` could print it without the "is".

evolve: move more of the progress-related variables together

evolve: delete dead calculation of number of troubled revisions The "count" variable is recalculated in the regular (no --continue) code path and it isn't used anywhere else (it used to be set to 1 in the --continue code path, but that now has its own progress counting).

evolve: drop nested locks and transactions All callers of _solveone() now take the locks and start the transactions, so there's no need to do that anymore.

next: start transaction before calling _solveone() All other callers do this, and I'm about to make _solveone() not create a transaction.

evolve: use single transaction also when continuing

evolve: run in a single transaction This speeds up `hg evolve --all` of a stack of 24 commits in the hg repo from 11.5s to 3.7s (3x). As can be seen in the tests, it also avoid some warnings about transiently unstable commits.

evolve: extract function for solving one revision, including merges Will make the next patch simpler.

evolve: mention that --all is the default behavior now