fileset: matchctx.existing() must consider unknown files stable

fileset: matchctx.existing() must consider unknown files

By default, unknown files are ignored. If the 'unknown()' predicate
appears in the syntax tree, then they are taken in account.
Unfortunately, matchctx.existing() was filtering against non-deleted
context files, which does not include unknown files. So:

  $ hg debugfileset 'binary() and unknown()'

would not return existing binary unknown files.

--- a/mercurial/fileset.py	Wed Aug 15 21:44:00 2012 +0200
+++ b/mercurial/fileset.py	Wed Aug 15 22:29:09 2012 +0200
@@ -432,10 +432,12 @@
     def existing(self):
         if self._status is not None:
             removed = set(self._status[3])
+            unknown = set(self._status[4])
         else:
             removed = set()
+            unknown = set()
         return (f for f in self.subset
-                if f in self.ctx and f not in removed)
+                if (f in self.ctx and f not in removed) or f in unknown)
     def narrow(self, files):
         return matchctx(self.ctx, self.filter(files), self._status)
 

--- a/tests/test-fileset.t	Wed Aug 15 21:44:00 2012 +0200
+++ b/tests/test-fileset.t	Wed Aug 15 22:29:09 2012 +0200
@@ -80,4 +80,9 @@
 
   >>> file('bin', 'wb').write('\0a')
   $ fileset 'binary()'
+  $ fileset 'binary() and unknown()'
+  bin
+  $ hg add bin
+  $ fileset 'binary()'
+  bin