initial pp constraint
Merge pull request #1240 from marqh/pp_constraint

PP constraint
Update whatsnew v171
Removed spurious line from whatsnew
Merge pull request #1246 from dkillick/update_whatsnew_v1-7-1

Update whatsnew doc for v1.7.1
Bump version to 1.7.1-rc.1
Bump version to 1.7.1-rc.1.DEV
Remove obsolete image results
Merge pull request #1261 from rhattersley/obsolete-images

Remove obsolete image results
Allow for variance in netCDF4 behaviour.
Merge pull request #1260 from rhattersley/netcdf-masking

Allow for variance in netCDF4 behaviour.
Switch to miniconda test environment.
Update image results for later freetype.