extract: parse 'nodeid' using the generic mechanism

Parsing 'nodeid' is very simple and a good first test.

mercurial/patch.py

@@ -155,6 +155,7 b' def split(stream):'
 # list of pairs ("header to match", "data key")
 patchheadermap = [('Date', 'date'),
                   ('Branch', 'branch'),
+                  ('Node ID', 'nodeid'),
                  ]
 
 def extract(ui, fileobj):
@@ -236,8 +237,6 b' def extract(ui, fileobj):'
                         if line.startswith('# User '):
                             data['user'] = line[7:]
                             ui.debug('From: %s\n' % data['user'])
-                        elif line.startswith("# Node ID "):
-                            data['nodeid'] = line[10:]
                         elif line.startswith("# Parent "):
                             parents.append(line[9:].lstrip())
                         elif line.startswith("# "):