xenstore: document the xenstore protocol
The attached patch adds a new text file docs/misc/xenstore.txt which
describes the actual protocol implemented by xenstored. This was
reverse-engineered from the actual code in tools/xenstore.
I didn't bother making any automatic arrangements to ensure that the
implemented and documented protocols are kept in step (for example,
automatic code generation, etc.) The protocol is rather messy
unfortunately and unsuitable for an xdr approach, and in any case is
not likely to change very quickly.
Also in this patch are a couple of comments for xenstored_core.c which
help clarify the behaviour of some payload parsing helper functions.
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>