VMM/maillocation: MailLocation.__init__(): take a 'format' name,
instead of a 'directory' name.
- added function known_format() to the module.
VMM/Account: Adjusted to above changes.
VMM/Account: Adjusted to changes in maillocation.MailLocation.
VMM/maillocation: Class MailLocation added missing property `mid`.
Added new error to VMM/constants/ERROR and doc/source/vmm_constants_error