Topbloke patch is:
	- branch in refs/topbloke-tips/<full-name>
		contains the working version, fast-forwarding
	- branch in refs/topbloke-bases/<full-name>
		contains the base version, being the pulling
		merge of all the bases

In-tree, there are metadata files in .topbloke

    Files which are per-patch and do not inherit any contents
    or changes from bases or dependencies:

	msg		patch "commit message"
			("# not applicable" in bases)

	deps		direct dependencies, one per line
			as either:
				<topbloke patch name>
				.f <ref name including refs/heads/>
				.tg <ref name not including refs/heads/>
			(empty in base branches)

	props		properties that apply to this patch, one per line
			 in the format "<name>[ <value>]" (exactly one
			 space) where value can contain spaces and
			 a missing value is distinct from a missing property
			 but value if present must be nonempty
			base has its own, perhaps different, set of props;
			 Unknown props starting with [a-z] are ok;
			 otherwise fatal.  Currently defined props:
		patch <name>	topbloke patch name (in tip and base)
		topgit <name>	this is a topgit import (in tip and base)
		Deleted		patch is deleted (in tip only, no value)

    Files which not inherit contents and changes from dependencies:

	included	actual included deps, one per line
				format as for deps

	pprops		properties that apply to this patch and all its
			dependencies (ie, properties that propagate)
			 Unknown props starting with [a-z] are ok;
			 otherwise fatal.  No currently defined props.


<full-name> has the format:
	<email>@<domain.name>/<yyyy>-<mm>-<dd>T<hh><mm><ss>Z/<nickname-path>
where nickname-path's first component must not start with a digit 
contain ~ or @  (: is not allowed in refs hence the squashing)
eg
	ijackson@chiark.greenend.org.uk/2012-01-20T225127Z/reorg/sponge
NB only exactly that date format is allowed and timezone must be Z.

Patches may be specified as
	[<qualifier>/...][<nickname-path-spec>]
where <qualifier>/ is one of
	[<email>]@[<domain.name>/
		Only patches matching the specified email local part
		or domain name match
	[<date-spec>/]
		A prefix of the ISO8601 date spec, stopping
		just after a numeric component (or at the end)
	[<approx-date-containing-~>/]
		Intepreted by date -d after ~s have been replaced by
		spaces.  When we come to select, take the patch
		nearest that date rather than the most recent


<nickname-path-spec> may be
	<nickname-path>
	./<nickname-new-leaf-component>
	../<nickname-path-spec>

<date-spec> may be
	<approximate date spec containing at least one ~>
		means all patches are candidates

So overall, if the current patch is
	ijackson@chiark.greenend.org.uk/2011-08-20T120320Z/fixes/pudding
then all of the following can refer to the same patch
	./sponge
	../reorg/sponge
	reorg/sponge
	2012/reorg/sponge
	2012/reorg/sponge
	2012/./sponge
	jan~/./sponge
	ijackson@/reorg/sponge
	ijackson@/2012/reorg/sponge
	ijackson@chiark.greenend.org.uk/reorg/sponge
	ijackson@chiark.greenend.org.uk/2012-01-20T225127Z/reorg/sponge

Search algorithm:
	1. prefer patches with email address (or domain)
	   matching current patch
	2. prefer patches with our own email address (or domain)
	3. other patches
Within this there may be patches with multiple dates; prefer the most
recent.