Merge pull request #781 from esc24/extract_fix

Extract fix
Merge pull request #782 from esc24/extract_fix_tuple_comp

Extract fix for Cell comparison
Provide utility function "file_is_newer_than" for results caching.
Simplify file load helper.
Added whats-new entry.  Slightly improved docstring.
Move 'tests.util.test_file_is_newer_than' into the unit-tests structure.
Tidied error case testing.
Changes for v1.5.1
Updated version to v1.5.1
Version updated to v1.5.2-dev
Merge pull request #789 from dkillick/Version_1.5.1

Version 1.5.1
Merge pull request #787 from pp-mo/pickle_helper

Provide utility function "file_is_newer_than" for results caching.
Move concatenate operation from 'iris.experimental' into a CubeList method.
Merge pull request #783 from pp-mo/promote_concat

Moved concatenate from 'iris.experimental' to 'iris'.
Switch to setuptools and pre-load coastlines.
 - The python-distribute.org DNS entry no longer exists.
 - The distribute package has been merged back into setuptools.
Merge pull request #795 from rhattersley/setuptools

Switch to setuptools.
Added rolling window support for masked arrays
Merge pull request #793 from niallrobinson/rolling_window_masked

rolling_window on masked cubes
NF - Load reduced regular lat/lon grids from GRIB1.
PEP 8 iris.unit