evolve: add an `--update` flag to `hg evolve` command This patch adds a new `--update` flag which defaults to True. The update flag updates the working directory to the head of evolved revisions after `hg evolve` command. This flag can be used to not update your working directory after `hg evolve` which has been one of the biggest feature request from fig team at Google. To not update your working directory, the user can do `hg evolve --no-update`. If the working directory get obsoleted by evolve command, it will update to the successor. This patch also adds some basic tests for the flag introduced.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
^tests/.*\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes

^docs/training/graphs/
^docs/training/html/
^docs/training/index.html
^docs/training/graphviz-images/
^docs/training/img/
^docs/training/output/
^docs/training/pandocfilters/