doc: add description about re-opening closed heads to 'Head, closed branch' in glossary

doc: fix careless document miss for term 'Close changeset' in glossary there is no term 'Changeset, close' in glossary. 'Close changeset' seems to have to be linked not to 'Branch, closed', but to 'Head, closed branch', because only the latter explains about "the changeset that marks a head as no longer interesting".

doc: fix careless document miss in help of hgext/notify according to configuration example below, and direction of changeset transference, this paragraph should describe about "changegroup" hook. [hooks] # one email for each incoming changeset incoming.notify = python:hgext.notify.hook # one email for all incoming changesets changegroup.notify = python:hgext.notify.hook # one email for all outgoing changesets outgoing.notify = python:hgext.notify.hook