[xen] Add a mutex around netif write,writev

We need this to avoid one packet write calling notify() while a parallel
writev has only written some of the fragments onto the ring.

This fixes the phenomenon where a packet fragments (eg containing HTTP
headers) end up being transmitted as whole frames. It also removes the
curious duplicates experienced during a ping flood.
Merge pull request #20 from djs55/fix-netfront-fragments

[xen] Add a mutex around netif write,writev
[xen] in netif, do not block until a response is received, but return right after the request has been successfully pushed and the other side notified
Sped up checksum calculation.
Merge pull request #21 from balrajsingh/master

checksum speed up
Well, there's good news and bad news.  To start with the bad news, there's a missing `-O3` in mirage-platform which led to the runtime being completely unoptimised on Xen. The good news is that we should be an awful lot faster now :)
release version 0.7.2
change xen installation to place libraries in a separate mirage-xen area, to avoid ocamlfind complaining about subdirectories in a package
add C stubs for the Str module, adapted to remove use of compatibility (e.g. stat_alloc to caml_stat_alloc).

We want to get rid of this eventually, but that can wait for namespaces and such
update CHANGES and bump to 0.8.0
0.8.0 CHANGES
With standard compiler, oS.cma gets now dynamically linked with unixrun. Fixes #require mirage;; in the toplevel.
Make ocamlfind to install libunixrun.so as well. This is necessary for mirage to work in the toplevel
Merge pull request #23 from vbmithr/master2

Fix mirage on the toplevel.
Fix the xenstore wait in blkif

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #25 from jonludlam/blkif-fix

Fix the xenstore wait in blkif
add CHANGES entry for #25
bump version to 0.8.1