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().
.. Common link and substitution definitions.
.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html