Add support for boolean comparisons in 'diff'

[lowell80]

Avoid producing output like this:

 [source]
-INDEXED = True
+INDEXED = 1
-INDEXED_VALUE = False
+INDEXED_VALUE = 0

Users should optionally be allowed to suppress identical boolean values on the diff CLI. We don't want to suppress these difference entirely, because sometimes a field looks like a boolean but really isn't, and we don't easily have access to a comprehensive list.

[lowell80]

Work started in 0403008.