extensions: add "uipopulate" hook, called per instance, not per process In short, this is the "reposetup" function for ui. It allows us to modify ui attributes without extending ui.__class__. Before, the only way to do that was to abuse the config dictionary, which is copied across ui instances. See the next patch for usage example.

hgweb: load globally-enabled extensions explicitly Before, extensions were loaded as a side effect of hg.repository() if the hgweb was executed as a CGI/WSGI. I want to make it explicit so that another ui hook can be inserted after extensions.loadall().