bash_completion: support GNU sed 3 and non-GNU sed
replaced command 'Q' introduced in GNU sed 4, in order to support
platforms with older sed.
#!/bin/sh
hg
hg -q
hg help
hg -q help
hg add -h
hg add --skjdfks
hg help diff
hg help status
hg -q help status
hg help foo
hg skjdfks
exit 0