Generalise regular interpolation.
Extended the env variables for Iris's travis-ci testing.
Review changes.
Fix cube.copy() for scalar cubes.
Merge pull request #1381 from rhattersley/generalise-interp

Generalise regular interpolation.
Ran the system tests with default tests on travis.ci.
Fix vector dims shape for scalar value
Merge pull request #1409 from pelson/doctest_separate

Extended the env variables for Iris's travis-ci testing.
Merge pull request #1412 from dkillick/fix_no_dims

Fix vector dims shape for scalar dims
Merge pull request #1411 from pp-mo/scalar_cube_copy

Fix cube.copy() for scalar cubes.
Remove unnecessary with_statement imports.

Iris requires Python 2.7, so the with statement is already enabled.
Add __future__ imports on all remaining files.

All these files should not be affected by these imports, so this is just
one big mass change. The files where these imports make a difference
were already changed in a previous commit.

Only the examples are exempt from the __future__ imports; this should make
things simpler for users, plus they have no real effect in these files.
Add coding standards test for __future__ imports.