phabricator: add the "Changes Planned" status name

I noticed this when coloring the status output.  But it looks like status names
are also used in the pseudo revset language as well, and abort when parsing a
name not in this list.

Differential Revision: https://phab.mercurial-scm.org/D7607

hgext/phabricator.py

@@ -1268,6 +1268,7 b' def _confirmbeforesend(repo, revs, oldma'
     b'needsrevision',
     b'closed',
     b'abandoned',
+    b'changesplanned',
 }