In reconcile_units, interpret no units as units of '1' ('fraction').  I may later remove this
feature if I think we don't need it.
Also, minor improvements to warning messages and comments.
fix a little bug - compare axis names with names, not with axes.
Merge pull request #27 from susburrows/susburrows/add_regions_support

Susburrows/add regions support
Insert select_region and interpret_region functions where appropriate in other reduction.py functions
Add default arguments to reduce_time_space_seasonal_regional
Refactor some code with generic functions and add delete_singleton_axis to select_lev function.
Refactor seasonal climatology functions -- try to push all special cases into one function.