svnsubrepo: decorate dirty method with annotatesubrepoerror

This function invokes svn commands which can error out in any number
of ways, so it's helpful to know in which subrepo this error happens.

mercurial/subrepo.py

@@ -1327,6 +1327,7 b' class svnsubrepo(abstractsubrepo):'
                     return True, True, bool(missing)
         return bool(changes), False, bool(missing)
 
+    @annotatesubrepoerror
     def dirty(self, ignoreupdate=False, missing=False):
         wcchanged = self._wcchanged()
         changed = wcchanged[0] or (missing and wcchanged[2])