purge: add -i flag to delete ignored files instead of untracked files
It's convenient for deleting build artifacts. Using --all instead
would delete other things too.
Differential Revision: https://phab.mercurial-scm.org/D8096
== New Features ==
* `hg purge`/`hg clean` can now delete ignored files instead of
untracked files, with the new -i flag.
== New Experimental Features ==
== Bug Fixes ==
== Backwards Compatibility Changes ==
== Internal API Changes ==
* The deprecated `ui.progress()` has now been deleted. Please use
`ui.makeprogress()` instead.
* `hg.merge()` has lost its `abort` argument. Please call
`hg.abortmerge()` directly instead.
* The `*others` argument of `cmdutil.check_incompatible_arguments()`
changed from being varargs argument to being a single collection.