LocationConfig should look for options on parent locations when they're not found

Let's say I have the following branches.conf file:

[/home/salgado/repo/foo]
public_repository = sftp://example.com/foo
pqm_branch = sftp://example.com/pqm/foo
pqm_email = <email address hidden>
[/home/salgado/repo/foo/somebranch]
push_location = sftp://example.com/foo/somebranch

If I look for a pqm_branch option on the [/home/salgado/repo/foo/somebranch] location, I'll get the global pqm_branch option, when in fact I'd like it to give the pqm_branch defined on the parent location.

This problem happened when I wrote my .branches.conf file to use together with the pqm-submit plugin, and then after that I did a bzr push --remember on one of my repo's branches. The result was a .branches.conf file similar to the above one, which prevents me from using pqm-submit, as it'll always use the default pqm_branch.