Restore 4.00.1 compatibility at the price of less succinct code

It was previously not working due to the use of record disambiguation
in the records.  This patch disambiguates everything such that it
remains compiling under 4.00.1.

(thanks to Jeremy Yallop for pointing out the source of the bug)
Add Travis back for 4.00.1
Sync CHANGES to reflect that 4.00.1 survives for another day
Update to new merged Io_page

The opam package 'io-page' will install two ocamlfind packages:

  io-page
  io-page.unix

A Unix app needs both, a xen app only needs io-page.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #194 from avsm/restore-4.00.1-compat

Restore 4.00.1 compat
Merge pull request #195 from djs55/new-merged-io-page

Update to new merged Io_page