VCS: Add diff pattern tests for CVS and Mercurial

* Fix Mercurial pattern
* Make fileNameFromDiffSpecification protected again (it was made
  public for running tests, but they are now run from VCSBaseEditor)
* Remove DiffHighlighter::filePattern(). Not used anymore.

Change-Id: Ifc99f761f0ab96cc79f1d018e3f3c8cf4603da10
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/cvs/cvsplugin.h

@@ -123,6 +123,10 @@ private slots:
     void uneditCurrentFile();
     void uneditCurrentRepository();
     void cvsDiff(const Cvs::Internal::CvsDiffParameters &p);
+#ifdef WITH_TESTS
+    void testDiffFileResolving_data();
+    void testDiffFileResolving();
+#endif
 
 protected:
     void updateActions(VcsBase::VcsBasePlugin::ActionState);