Version control: Improve detection.

Merge managesDirectory() and findTopLevelForDirectory()
into one giving managesDirectory() an optional topLevel
parameter. This removes the need to go up the directory
hierarchy twice when checking for Merurial or git and also
saves some checks for CVS/Subversion.
VCSManager: Check cache in reverse order starting out with
the full path first to improve handling of nested repositories.
Rubber-stamped-by: con
Acked-by: dt

src/plugins/coreplugin/iversioncontrol.h

@@ -56,21 +56,12 @@ public:
     /*!
      * Returns whether files in this directory should be managed with this
      * version control.
+     * If \a topLevel is non-null, it should return the topmost directory,
+     * for which this IVersionControl should be used. The VCSManager assumes
+     * that all files in the returned directory are managed by the same IVersionControl.
      */
-    virtual bool managesDirectory(const QString &filename) const = 0;
 
-    /*!
-     * This function should return the topmost directory, for which this
-     * IVersionControl should be used. The VCSManager assumes that all files in
-     * the returned directory are managed by the same IVersionControl.
-     *
-     * Note that this is used as an optimization, so that the VCSManager
-     * doesn't need to call managesDirectory(..) for each directory.
-     *
-     * This function is called after finding out that the directory is managed
-     * by a specific version control.
-     */
-    virtual QString findTopLevelForDirectory(const QString &directory) const = 0;
+    virtual bool managesDirectory(const QString &filename, QString *topLevel = 0) const = 0;
 
     /*!
      * Called to query whether a VCS supports the respective operations.