xapi: Change optdir to /usr/lib/xapi

Signed-off-by: Euan Harris <euan.harris@citrix.com>
ocaml-oclock: Fix build dependency on ocaml-findlib-devel

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #186 from euanh/build-improvements

Dependency and path tweaks