FINALLY got the usage messages working

this fixes `vc help mycustomcommand`
but it still doesn't list `mycustomcommand` when you do `vc commands`, so that part still needs work
added an actual automated test (gasp!) for making sure the file specs are correct in the usage message
this involved a couple of cheap hacks which I'm not proud of
in my defense I can only point you at the guts of App::Cmd / MooseX::App::Cmd ... it's scary in there, man!
silly barefootcoder, validation attributes aren't required for custom commands ...