[RFC][BBC] New revision serializer

[Jelmer Vernooij]

The attached patch adds a new serializer format that no longer uses XML
but instead a simple plain-text format. This format is a bit faster than
 the old XML format (1M roundtrips in 3s vs 14s here), and most
importantly now supports certain characters that can't be escaped in XML
. This patch already passes all but one test in the testsuite when
applied to brisbane-core.

An example serialized revision would look like this:

<<<

revision-id: jelmer at samba.org-20090401175407-cbhi14v5rx4qbt47
timestamp: 1238608447
parent-ids: john at arbash-meinel.com-20090331170410-sxpic3huylfctxu2
inventory-sha1: 6164b2b8683a0a5666d3f7a6a67bb2d0bf62410f
committer: Jelmer Vernooij <jelmer at samba.org>
timezone: 7200
property: branch-nick=rev-serializer
message: Add simple revision serializer.

Passes all but one test.

>>>

I've tried to group the data that is most likely to re-appear in
different revisions (committer, timezone, properties, message).

Does this format look reasonable?

Cheers,

Jelmer