vhd-format.0.7.1 and vhd-tool.0.7.5

Signed-off-by: David Scott <dave.scott@citrix.com>
sha.1.9: build on FreeBSD from vincenthz/ocaml-sha#12
Merge pull request #2320 from dsheets/master

sha.1.9: build on FreeBSD from vincenthz/ocaml-sha#12
+uri.1.7.1
Merge pull request #2311 from djs55/vhd

vhd-format.0.7.1 and vhd-tool.0.7.5
Merge pull request #2321 from avsm/master

+uri.1.7.1
+cstruct.1.3.0
Merge pull request #2322 from avsm/master

+cstruct.1.3.0
Merge branch 'master' of github.com:OCamlPro/opam-repository into external-minios