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.
1:016807e6fdaf
0:eb43f19ff115
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
eb43f19ff115
eb43f19ff115+
reverting file1
? file1.orig
eb43f19ff115
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip