Merge pull request #357 from esc24/travis_grib

Use position independent code flag for compilation of gribapi
Basic support for varying longitude ranges.
Merge pull request #350 from rhattersley/wrap-linear

Basic support for varying longitude ranges.
Changes for rc1.
Revert Iris version from 1.2.0-rc1 back to 1.2.0-dev.
Default tests to the 'agg' matplotlib backend.
Update module docstring
Modified cube.summary() to handle unicode cube attributes.