subrepo: don't exclude files in .hgignore when adding to git

The previous test gave a false success because only an hg-ignored pattern was
specified.  Therefore match.files() was empty, and it fell back to the files
unknown to git.  The simplest fix is to always consider what is unknown to git,
as well as anything specified explicitly.  Files that are ignored by git can
only be introduced by an explicit mention in match.files().

mercurial/subrepo.py

@@ -1526,14 +1526,15 b' class gitsubrepo(abstractsubrepo):'
     def add(self, ui, match, prefix, explicitonly, **opts):
         if self._gitmissing():
             return []
-        if match.files():
-            files = match.files()
-        else:
-            (modified, added, removed,
-             deleted, unknown, ignored, clean) = self.status(None)
-            files = unknown
+
+        (modified, added, removed,
+         deleted, unknown, ignored, clean) = self.status(None)
 
-        files = [f for f in files if match(f)]
+        # Unknown files not of interest will be rejected by the matcher
+        files = unknown
+        files.extend(match.files())
+
+        files = [f for f in sorted(set(files)) if match(f)]
         for f in files:
             exact = match.exact(f)
             command = ["add"]

tests/test-subrepo-git.t

@@ -922,11 +922,11 b' make sure everything is reverted correct'
   > *.python
   > EOF
   $ hg add .hgignore
-  $ hg add --subrepos "glob:**.python"
+  $ hg add --subrepos "glob:**.python" s/barfoo
   adding s/snake.python (glob)
   $ hg st --subrepos s
+  A s/barfoo
   A s/snake.python
-  ? s/barfoo
   ? s/c.c
   ? s/cpp.cpp
   ? s/foobar.orig