Enhanced guess_bounds docstring.
Fix masked npy reference file creation.
Merge pull request #759 from rhattersley/fix-masked-npy-data

Fix masked npy reference file creation.
Merge pull request #756 from pp-mo/guess_bounds_reword

Enhanced guess_bounds docstring.
Merge branch 'master' of https://github.com/SciTools/iris into cube_explorer
Changed broadcast_weights to broadcast_array