deprecate cube iteration.
 : test included
revised cube iteration warning + test
 : clearer test code
 : don't use DeprecationWarning
Fixed issue introduced by #300.
Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
Merge pull request #310 from pelson/fix_merge_bug

Fixed issue introduced by #300.
Tidy cube.__iter__ docstring.
Tweak docstring and comments
Merge pull request #273 from pp-mo/no_cube_iter

control cube iteration
Merge pull request #311 from rhattersley/cell-comparison

Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
Merge remote branch 'upstream/v1.1.x'

* upstream/v1.1.x:
  Tweak docstring and comments
  Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
Updated the extests to easily support image tolerances.
Updated tolerances.
Renamed the result image.
Re-added the missing extest image.
Review action.
Merge pull request #316 from pelson/extest_simplification

Updated the extests to easily support image tolerances.
extest_remove_unused_import
Merge pull request #326 from iedwards/extest_remove_unused_import

Unused "import unittest" removed from extests