mq: write '# Parent ' lines with two spaces like export does (BC)

This aligns "Parent" node IDs with "Node ID" node IDs.

hgext/mq.py

@@ -150,7 +150,7 b' class patchheader(object):'
                 elif line.startswith("# Date "):
                     date = line[7:]
                 elif line.startswith("# Parent "):
-                    parent = line[9:].lstrip()
+                    parent = line[9:].lstrip() # handle double trailing space
                 elif line.startswith("# Branch "):
                     branch = line[9:]
                 elif line.startswith("# Node ID "):
@@ -232,7 +232,8 b' class patchheader(object):'
         self.date = date
 
     def setparent(self, parent):
-        if not self.updateheader(['# Parent '], parent):
+        if not (self.updateheader(['# Parent  '], parent) or
+                self.updateheader(['# Parent '], parent)):
             try:
                 patchheaderat = self.comments.index('# HG changeset patch')
                 self.comments.insert(patchheaderat + 1, '# Parent ' + parent)