tools/ocaml: Rename the ocaml libraries

tools/ocaml: Rename the ocaml libraries

ocamlfind does not support namespaces, so to avoid
name clashes the module names have become longer.
Additionally, the xenstore and xenbus subdirs, which
contain several modules each, have been packed into
toplevel Xenstore and Xenbus modules.

xb becomes xenbus, xc becomes xenctrl, xl becomes xenlight,
xs becomes xenstore, eventchn becomes xeneventchn and
mmap becomes xenmmap.

[ Patch modified from that submitted, to update the .hgignore, and to
  cope with intervening changes to mmap_stubs.c -iwj ]

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>