BUG: Fix broken test result TestAtlanticProfiles

This commit increases the graphic tolerance this specific tests.
Visual comparison of the test failure has been made and confirmation
that it is correct.
lamb/polar coord untis
Merge pull request #698 from bblay/lambunit

lamb/polar coord units
ENH: Allow cube slicing by dimension index

Currently only coordinates can be used to slice a given cube.  Since
coordinates are not allways associated with dimensions of a cube, the
ability to specify dimension and or mix of coordinate and dimension is
added here to facilitate use.
Merge pull request #671 from cpelley/fix_atlanticprof_test

BUG: Fix broken test result TestAtlanticProfiles
Merge pull request #553 from cpelley/friendly_slicing

Add ability to pass data dimensions for slicing cube
Limit unit calendar argument