bash_completion: don't complete export with "garbage" when mq is not around
The "garbage" is the output of hg help printed when a command is not found.
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)