Wire-protocol featureset- and code-unification

[Sune Foldager]

I wrote the initial version of a working document on unifying the two
wire protocols, and later on the underlying code supporting them. Please
read and let's discuss what to do.

Immediate motivation for me: I want to advance the implementation of
light-weight copies, which I (very slightly) started looking at at the
sprint. The changesets originate from Vsevolod Solovyov, but he didn't
get around to implemting the wire-bits.

http://mercurial.selenic.com/wiki/WireProtocolUnificationPlan

/Sune