BUG: Fixed exclusion list

Currently iris test coding standards will perform pep8 checks on files
contained within the build directory and then ignore the results.  This
commit removes this checking entirely and fixes a bug present in
generating the assumed directory for the iris repository from the iris
path (a problem which arises when considering softlink vs real paths).
Ingest MetaRelate generated GRIB/CF mappings.
Fix parsing of filenames with colons

Fixes #872
Opt-in to Coord.cell returning time objects
Test tweaks
Rename cell_time_objects to cell_datetime_objects
Merge pull request #883 from rhattersley/date-cells

Opt-in to Coord.cell returning time objects
Merge pull request #877 from shoyer/fix-file-schemes

Fix parsing of filenames with colons
Add PP load + save support for potential-temperature vertical levels.
Review changes.
Merge pull request #886 from pp-mo/tpot_levels

Add PP load + save support for potential-temperature vertical levels.
Add PartialDateTime
Merge pull request #885 from rhattersley/partial

Add PartialDateTime
Experimental regrid.
Unicode tests updated, new reference string files added
Merge pull request #873 from bjlittle/orca_to_atmos

Experimental regrid.
Review actions: comment added, sys module introduced now explicitly removed at contextmgr exit
Added options for fileformats.netcdf.save

Adds new options for saving netCDF files to allow for
custom unlimited dimensions and saving netCDF4 files with
compression.

See discussion in #860.
Changed unlimited dimensions to use coordinate names

Sorry about that!
Fixed failing unit tests