Whitespace: Tidy up update_table function

$ camlp4o -printer o -no_comments ocaml/xapi/export.ml | md5sum
fc1825315a9036f85b1741ffd30b64b0  -
$ git co HEAD^
$ camlp4o -printer o -no_comments ocaml/xapi/export.ml | md5sum
fc1825315a9036f85b1741ffd30b64b0  -

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Don't create refs for snapshots that don't exist on import

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Check that ref is valid, not just that it is not null

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #2040 from simonjbeaumont/sxm-failure-fix

Don't rewrite Refs for snapshots that don't exist