A lot of times, I need to update to some other cset with dirty working
directory. Good number of times, I run hg shelve and hg update in order.
Let's add --shelve flag to hg update which will shelve wdir changes before
running the update.
.. feature::
`--shelve` flag to `hg update` if shelve extension is enabled. The flag will shelve working directory changes before performing update.
It's not clear that this is related to --shelve. Can we instead first check if the working is dirty? Or make this message more explicit. The former seems better if you think users (including you) will want to set defaults.update=--shelve.