subrepo: add basestate method

This will allow us to sort out what's going on with state .hgsubstate
files more precisely.

mercurial/subrepo.py

@@ -275,6 +275,11 b' class abstractsubrepo(object):'
         """
         raise NotImplementedError
 
+    def basestate(self):
+        """current working directory base state, disregarding .hgsubstate
+        state and working directory modifications"""
+        raise NotImplementedError
+
     def checknested(self, path):
         """check if path is a subrepository within this repository"""
         return False
@@ -446,6 +451,9 b' class hgsubrepo(abstractsubrepo):'
             return True
         return w.dirty() # working directory changed
 
+    def basestate(self):
+        return self._repo['.'].hex()
+
     def checknested(self, path):
         return self._repo._checknested(self._repo.wjoin(path))
 
@@ -666,6 +674,9 b' class svnsubrepo(abstractsubrepo):'
                 return False
         return True
 
+    def basestate(self):
+        return self._wcrev()
+
     def commit(self, text, user, date):
         # user and date are out of our hands since svn is centralized
         changed, extchanged = self._wcchanged()
@@ -907,6 +918,9 b' class gitsubrepo(abstractsubrepo):'
         out, code = self._gitdir(['diff-index', '--quiet', 'HEAD'])
         return code == 1
 
+    def basestate(self):
+        return self._gitstate()
+
     def get(self, state, overwrite=False):
         source, revision, kind = state
         if not revision: