VMM/account: Fixed account's transport check.
Make sure that 'virtual:' isn't used as transport when the mailbox-format
is set to mdbox or sdbox.
..|curr_vers_rel_date|replace:: The most current version of vmm is 0.6.0, released on 28 June 2012...|rel_hist|replace:: Older releases are listed in the :doc:`release_history`.