Thanks @pp-mo for offline chatting, and to @rhattersley.
If we can dig out a copy of _area-type-table.xml_, I suggest we add it to the Iris codebase,
and stop calling this cfchecker script, using instead a call to cfchecks with pointers to the Iris version.

Advantages:
 - no deps on breakable web resource
 - anyone can run these tests, not just ukmo & travis

Any objections?