gendoc: automatically create help for default extensions.
Adds a section in the hg.1 manpage and corresponding hg.1.html
file. Each extension is listed with its module docstring, followed by
the commands defined by that extendsion.
Creates help for extensions by extracting doc strings from the extension modules
and its commands.
Test update logic when there are renames
Update with local changes across a file rename
$ hg init
$ echo a > a
$ hg add a
$ hg ci -m a
$ hg mv a b
$ hg ci -m rename
$ echo b > b
$ hg ci -m change
$ hg up -q 0
$ echo c > a
$ hg up
merging a and b to b
warning: conflicts during merge.
merging b failed!
0 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
[1]
$ cd ..