context.walk: walk all files when file and '.' given

When both '.' (the working copy root) and an explicit file (or files)
are in match.files(), we only walk the explicitly listed files. This
is because we remove the '.' from the set too early. Move later and
add a test for it. Before this change, the last test would print only
"3".

mercurial/context.py

@@ -588,10 +588,6 b' class changectx(basectx):'
 
     def walk(self, match):
         fset = set(match.files())
-        # for dirstate.walk, files=['.'] means "walk the whole tree".
-        # follow that here, too
-        fset.discard('.')
-
         # avoid the entire walk if we're only looking for specific files
         if fset and not match.anypats():
             if util.all(fn in self for fn in fset):
@@ -606,6 +602,9 b' class changectx(basectx):'
                 fset.remove(fn)
             if match(fn):
                 yield fn
+        # for dirstate.walk, files=['.'] means "walk the whole tree".
+        # follow that here, too
+        fset.discard('.')
         for fn in sorted(fset):
             if not self.hasdir(fn):
                 match.bad(fn, _('no such file in rev %s') % self)

tests/test-cat.t

@@ -22,10 +22,22 b''
   $ hg cat -r 1 b
   1
 
-Test fileset
+Test multiple files
 
   $ echo 3 > c
   $ hg ci -Am addmore c
+  $ hg cat b c
+  1
+  3
+  $ hg cat .
+  1
+  3
+  $ hg cat . c
+  1
+  3
+
+Test fileset
+
   $ hg cat 'set:not(b) or a'
   3
   $ hg cat 'set:c or b'