Revoked the deprecation of return values from callbacks.
Added @ajdawson's excellent observations.
Added the callback unit tests.
Fix bug in comparison with netcdftime.datetime
Add PartialDateTime.__repr__ and update copyright periods.
Merge pull request #918 from rhattersley/fix-pdt-with-netcdftime

Fix bug in comparison with netcdftime.datetime
Separate data/mask in PP repr
Fix date formatting to work with NumPy 1.7
Merge pull request #910 from pelson/revoke_callback_interface_deprecation

Revoked the deprecation of return values from callbacks.
Fix pandas array order for numpy 1.7
Merge pull request #920 from rhattersley/numpy-1.7-date-arrays

Fix date formatting to work with NumPy 1.7
Normalise array order after circular interpolation.
Normalise array order from ABF loader.
Merge pull request #927 from rhattersley/numpy-1.7-abf-order

Normalise array order from ABF loader.
Normalise array order after curl.
Merge pull request #923 from rhattersley/numpy-1.7-masked-pp

Separate data/mask in PP repr
Merge pull request #925 from rhattersley/numpy-1.7-pandas-order

Fix pandas array order for numpy 1.7
Make pandas sharing check compatible with numpy 1.7
Merge pull request #926 from rhattersley/numpy-1.7-circular-order

Normalise array order after circular interpolation.
Merge pull request #929 from rhattersley/numpy-1.7-curl-order

Normalise array order after curl.