mq: record more data in patchheader class (no behavior changes)

* parse branch and nodeid header lines
* remember the line number where diffs started

Combined, these make mq.patchheader() very useful for parsing and
preserving a patch header through edits. TortoiseHg will use the
nodeid and parent to display these header datums in the graph when
patches are unapplied, and uses diffstartline to parse patch files
using record.parsepatch().

hgext/mq.py

@@ -86,6 +86,8 b' class patchheader(object):'
         parent = None
         format = None
         subject = None
+        branch = None
+        nodeid = None
         diffstart = 0
 
         for line in file(pf):
@@ -106,6 +108,10 b' class patchheader(object):'
                     date = line[7:]
                 elif line.startswith("# Parent "):
                     parent = line[9:]
+                elif line.startswith("# Branch "):
+                    branch = line[9:]
+                elif line.startswith("# Node ID "):
+                    nodeid = line[10:]
                 elif not line.startswith("# ") and line:
                     message.append(line)
                     format = None
@@ -134,6 +140,9 b' class patchheader(object):'
 
         eatdiff(message)
         eatdiff(comments)
+        # Remember the exact starting line of the patch diffs before consuming
+        # empty lines, for external use by TortoiseHg and others
+        self.diffstartline = len(comments)
         eatempty(message)
         eatempty(comments)
 
@@ -147,6 +156,9 b' class patchheader(object):'
         self.user = user
         self.date = date
         self.parent = parent
+        # nodeid and branch are for external use by TortoiseHg and others
+        self.nodeid = nodeid
+        self.branch = branch
         self.haspatch = diffstart > 1
         self.plainmode = plainmode