--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -231,6 +231,16 @@ class dirstate(object):
         except IOError, err:
             if err.errno != errno.ENOENT: raise
 
+    def reload(self):
+        def mtime():
+            m = self.map and self.map.get('.hgignore')
+            return m and m[-1]
+
+        old_mtime = self.ignorefunc and mtime()
+        self.read()
+        if old_mtime != mtime():
+            self.ignorefunc = None
+
     def copy(self, source, dest):
         self.lazyread()
         self.markdirty()