uncommit: use field names instead of field numbers on scmutil.status

As part of my pytype adventures I want to make scmutil.status no longer a
subclass of tuple. This is part of that process.

Differential Revision: https://phab.mercurial-scm.org/D7395

hgext/uncommit.py

@@ -157,7 +157,8 b' def uncommit(ui, repo, *pats, **opts):'
 
     with repo.wlock(), repo.lock():
 
-        m, a, r, d = repo.status()[:4]
+        st = repo.status()
+        m, a, r, d = st.modified, st.added, st.removed, st.deleted
         isdirtypath = any(set(m + a + r + d) & set(pats))
         allowdirtywcopy = opts[
             b'allow_dirty_working_copy'