Removes 'bc' disttype.

Makes 'block_size' optional for the cyclic dist_type.  When
'block_size' is absent or equal to one, equivalent to the conventional
'cyclic' dist type.
Merge pull request #36 from enthought/feature/remove-bc-disttype

Removes 'bc' disttype.
Merge branch 'feature/remove-bp-disttype'
Formatting fixes, indentation touchups.