mq: add qdelete --forget option
This removes an applied patch from the series and status files without
popping it. It is useful when an mq patch has been applied upstream.
#!/bin/shhg init aecho a > a/ahg --cwd a ci -A -m ahg clone a becho b > b/bhg --cwd b ci -A -m bchmod 100 a/.hghg --cwd b push ../achmod 700 a/.hg