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/sh
hg init t
cd t
echo foo > a
hg add a
hg ci -m "initial" -d "0 0"
echo foo > .hg/branch
hg ci -m "add branch name" -d "0 0"
echo bar > .hg/branch
hg ci -m "change branch name" -d "0 0"
rm .hg/branch
hg ci -m "clear branch name" -d "0 0"
hg co foo
cat .hg/branch
echo bleah > a
hg ci -m "modify a branch" -d "0 0"
hg merge
cat .hg/branch
HG_MERGE=true hg ci -m "merge" -d "0 0"
hg log
echo % test for invalid branch cache
hg rollback
hg tip