PEP8 conformance for iris.util.
Support grid code 11
ENH: Warning for collapsing lat-lon without weights
Review actions
Correction for review actions
Factored out grid selection
Review action corrections
Further review actions taken.
Reintroduced asser userwarning check
Merge pull request #834 from ajdawson/util-pep8

PEP8 conformance for util.py
Merge pull request #840 from rhattersley/ff-grid-11

Support FieldsFile grid code 11
Merge pull request #843 from cpelley/spatial_weights_v2

ENH: Warning for collapsing lat-lon without weights
Minor changes to allow simple broadcasting in cube addition and subtraction