NF - Load reduced regular lat/lon grids from GRIB1.
NF - Generalise reduced GRIB loading to versions 1 and 2.

Also adds support for missing values and changes the interpolation
method to 1d linear interpolation along constant latitudes.
Fakeup file modification times with larger intervals for test_file_is_newer_than.
Fix to timestamp setting code.
Merge pull request #738 from ajdawson/reduced-grib-load

Load reduced grids from GRIB
Merge pull request #806 from pp-mo/file_newer_fixtimes

Fake file timestamps with larger intervals for test_file_is_newer_than
Add extra grib2/cf translations : Fix bug in grib_phenom_translation.
(from review) extra tests for new grib phenomenon translations.