[PATCH 0 of 1] Add a -e/--edit option to 'hg tag'

[Steve Losh]

The 'hg tag' command lets you specify a custom message with '-m', but doesn't
have a way to use your editor for a longer message. This patch adds
a '-e/--edit' option (similar to qrefresh's).

This can be useful if you want to tag a release and add a list of changes since
the last release in the commit message, for example.

A test of the new option is also added.