Don't append trailing slash to maildir foldernames
Don't append trailing slash to maildir foldernames

When sep='/' in a Maildir, we were doing a os.path.join(dirname,'') on
the top level maildir, which results in a "dirname/", so all our maildir
folder names had slashes appended. Which is pretty much wrong, so this
fixes it by only using os.path.join when we actually have something to
append.

Signed-off-by: Sebastian Spaeth <98dcb2717ddae152d5b359c6ea97e4fe34a29d4c@SSpaeth.de>

frioux/offlineimap,frioux/offlineimap