mu4e: add custom variable for list of visible header flags - take 2
support recursive maildirs
support recursive maildirs
Merge branch 'recursive_maildirs' of https://github.com/nicolasavru/mu into recursive_maildirs

rebase to master
Merge pull request #178 from nicolasavru/recursive_maildirs

* improved recursive maildir support
Merge pull request #180 from abend/master

Customize visible header flags take 2.1
* mu4e:	small cleanup