Add a PRECISE_INDEXING flag to Distribution.

See inline comment for a full description.
Remove extra space in error string.
Rename applied function to be more descriptive.
Make PRECISE_INDEXING into a property.

This way I don't need to add it separately to all the constructors.  There's also the small benefit of resilience to changing out the underlying maps.
Restrict usage of LocalArrays' checked_getitem.
Fix a typo in a comment in a test.

Incidental.
Do the same for setitem.
Remove some debugging statements.
Remove the vestigial `checked_*item`s from LocalArray.

A copy of them had already been added to LocalArray's GlobalIndex object, I just had to use it.
Make a comment into a docstring.
PRECISE_INDEXING -> has_precise_index
Merge branch 'master' into refactor/restrict-use-of-checked-getitem

Conflicts:
	distarray/dist/maps.py
Update comments.
Merge pull request #377 from enthought/refactor/restrict-use-of-checked-getitem

Restrict use of checked_{g,s}etitem