mq: extend support for the --mq argument to extension commands
This allows commands like `purge' to accept the --mq option.
#!/bin/sh
# test that a commit clears the merge state.
hg init repo
cd repo
echo foo > file
hg commit -Am 'add file'
echo bar >> file
hg commit -Am 'append bar'
echo % create a second head
hg up -C 0
echo baz >> file
hg commit -Am 'append baz'
echo % failing merge
HGMERGE=internal:fail hg merge
echo resolved > file
hg resolve -m file
hg commit -m 'resolved'
echo % resolve -l, should be empty
hg resolve -l
# test crashed merge with empty mergestate
mkdir .hg/merge
touch .hg/merge/state
echo % resolve -l, should be empty
hg resolve -l