soft_repo.gl: Rename the release/* branches to distro/*.

The rationale here is to make it more apparent to maintainers that the
branches are not per-local-release version, but for major distro
releases should any updates need to be pushed to stable releases.

Due to the history, we will import software with previous Mandriva and
MES distro branches, which the import script helpfully renames for us to
distro/mdv* and distro/mes* appropriately. For our own distro branches
in the future, we should name them distro/mga*
soft_repo.gl: Allow topic branches.

While we may not use these too much in the future, we will need them for
importing branches from subversion.

The use of the term "topic" here is somewhat arbitrary but it avoids
cluttering up the main namespace and allows us to restrict things and
preserve some semblence of order :)
Version 0.9
Simplify how the noemail option works

Just use it to suppress the hooks.mailinglist git config value
thus allowing us to use the upstream post-receive-email hook directly.
Version 0.10
Include config values in quotes (it just feels nicer)

Also enclose the maintainer nick in square brackets as gitolite is fine with these and it
looks better than a hyphen as a separator.
Give $r instead of $r->{repos} as argument to load_gitrepos_dir

This will make it possible to create groups from load_gitrepos_dir.