serve: allow --daemon-postexec to be 'unlink:path' or 'none'
This patch changes the format of value of --daemon-postexec. Now it can be
either to unlink a file, or a no-op. The following patch will make chg to
use the no-op option.
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..