pep8
Do not clone closed branches by default.

Fixes #80.

This is a controversial fix in some ways; an earlier commit explicitly turned on cloning of closed branches. However, I feel that the default should be to not clone closed branches. There are a few reasons for this.

The main one is that a closed branch in mercurial is generally considered the equivalent of a deleted branch in git. Therefore, we do not want the deleted branch in git.

A second one is that cloning closed branches can take a great deal of time that is, for the above reason, completely wasted.

A third one is that we have a few problems with branch naming (eg #78, #75, #62) that are caused by conflicting branched names. This fix does not solve those issues, but when the conflicting branches are closed branches, it does prevent them from causing a clone to fail outright.