added tests for GRIB ProductDefinition 4.9 and to fail unrecognised PDTs
tidied new tests and revised for different proposed solution
added partial support for GRIB2 PDT4.9 ; tidied test_grib_load
fix test comment in test_grib_load
grib_rules.txt: tidied string formatting
test_grib_load.py:
  added comments highlightling partial PDT4.9 support
  fix bug in temporary file management : use 'unittest.temp_filename' in preference to 'tempfile'
  use unittest.temp_filename in place of tempfile methods
  various PEP8 fixes for layout + naming
Fixed iris.unit to use the correct ctype types.
Worked on formatting the changes for OSX support.
test_hybrid and test_merge to use smaller resource files
small changes
 : rename results file
 : drop real-data test in test_hybrid
rebased and resolved CML conflicts
Constraint extract slice optimisation.
Fieldsfile ancillary loading capability with PP LBTIM=2 support.
Closes #154 and closes #228.
Merge pull request #225 from bjlittle/constraint_extract

Constraint extract slice optimisation.
Merge pull request #243 from bjlittle/ff_ancillary

Fieldsfile ancillary loading capability with PP LBTIM=2 support.
Merge pull request #231 from pp-mo/externalise_tests_2_merge_n_hybrid

Externalise tests take-2 : "test_merge" + "test_hybrid"
Coordinate CML id sorted for attribute dictionary.
Review actions.
Merge pull request #253 from bjlittle/coord_xml_id

Coordinate CML id sorted for attribute dictionary.
Merge pull request #246 from pelson/unit_osx

unit.py on osx
BF - fix typo in udunits2 library locator