fileset: don't abort when running copied() on a revision with a removed file

It looks like AND with any status-y fileset would trigger this, as added() and
removed() also failed.  The 4.5-rc revision is a convenient test case, but the
merge isn't necessary.

mercurial/fileset.py

@@ -464,9 +464,10 b' def copied(mctx, x):'
     getargs(x, 0, 0, _("copied takes no arguments"))
     s = []
     for f in mctx.subset:
-        p = mctx.ctx[f].parents()
-        if p and p[0].path() != f:
-            s.append(f)
+        if f in mctx.ctx:
+            p = mctx.ctx[f].parents()
+            if p and p[0].path() != f:
+                s.append(f)
     return s
 
 @predicate('revs(revs, pattern)')

tests/test-fileset.t

@@ -249,6 +249,8 b' Test files properties'
 Test merge states
 
   $ hg ci -m manychanges
+  $ hg file -r . 'set:copied() & modified()'
+  [1]
   $ hg up -C 0
   * files updated, 0 files merged, * files removed, 0 files unresolved (glob)
   $ echo c >> b2