topicmap: move the monkey patching into a context manager
There is a couple of other place doing branchmap/topicmap update (of the served
set), we'll have to set the monkey patching for them.
This changeset is just doing the move to a context manager to make sure it is
correct.
# topics
Topics are an experiment to see if maybe the workflow defined by git
branches and hg bookmarks is only partially what users want - perhaps
something that feels more like a traditional VCS branch is right, but
that it should "dissolve" upon being finished. This extension exists
to be a sandbox for that experimentation.
# usage
Enable topics like any mercurial extension: download the source code to a
local directory, and add that directory to your `.hgrc`:
[extensions]
topics=path/to/hg-topics/src