This patch adds two new namespaces which will be enabled by remotenames
extension. The namespaces are remotebookmarks and remotebranches. Adding them
as namespaces will show them in various commands' output such as log, show work.
This will also unable to access changesets using that name.
Tests are also added for the same.
This is a part of moving hgremotenames extension to core.
hgremotenames: https://bitbucket.org/seanfarley/hgremotenames
Hm, I'm not sure if we want to name remote{bookmarks,branches} the same as local ones in log output. It may make sense to defer this until after the freeze, or else mark the remotenames extension as experimental for a cycle.