forget: show warning messages for forgetting in subrepo correctly

in 'cmdutil.forget()':

   for f in match.files():
       if match.exact(f) or not explicitonly:
           ....

is equal to:

   for f in match.files():
       if True:
           ....

because 'f' from 'match.files()' should 'match.exact(f)':

    - 'match.files()' returns 'self._files'
    - 'match.exact(f)' examines 'f in self._fmap',
    - 'self._fmap' of match is 'set(self._files)'

then, 'explicitonly' wants to suppress warning messges, if it is true
(= 'cmdutil.forget()' is invoked from 'subrepo.forget()').

so, current code should be fixed as:

    if not explicitonly:
        for f in match.files():
           ....

mercurial/cmdutil.py

@@ -1224,8 +1224,8 b' def forget(ui, repo, match, prefix, expl'
             ui.status(_("skipping missing subrepository: %s\n")
                            % join(subpath))
 
-    for f in match.files():
-        if match.exact(f) or not explicitonly:
+    if not explicitonly:
+        for f in match.files():
             if f not in repo.dirstate and not os.path.isdir(match.rel(join(f))):
                 if f not in forgot:
                     if os.path.exists(match.rel(join(f))):

tests/test-subrepo-recursion.t

@@ -195,10 +195,14 b' Test explicit path commands within subre'
   $ hg add foo/bar/z2.txt
   $ hg status -S
   A foo/bar/z2.txt
-This is expected to forget the file, but is currently broken
   $ hg forget foo/bar/z2.txt
   $ hg status -S
   ? foo/bar/z2.txt
+  $ hg forget foo/bar/z2.txt
+  not removing foo/bar/z2.txt: file is already untracked
+  [1]
+  $ hg status -S
+  ? foo/bar/z2.txt
   $ rm foo/bar/z2.txt
 
 Log with the relationships between repo and its subrepo: