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.
#!/bin/shhg init aecho a > a/ahg --cwd a ci -A -m ahg clone a becho b > b/bhg --cwd b ci -A -m bchmod 100 a/.hghg --cwd b push ../achmod 700 a/.hg