MNT : removed XR_data

 - a ndarray subclass that did not quite pan out
ENH : dict sub-class which has verbose exception

added verbosedict

 - overrides __getitem__ to provide a more verbose KeyError
 - for small numbers of keys (<25) lists them all in the error message
 - for large numbers, tells you how many there are
TST : added tests for verbose dict
TST/BUG : fix re-raise issue
Merge pull request #135 from tacaswell/core_work

Core work