Make completion for debugindex<tab><tab> show debugindexdot, too.
The special handling for commands with names that are substrings of other
commands (e.g. with st and strip) wasn't used with debug commands before.
#!/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