Drop rules on data_file_type attribute and replace with
rules on specific types, coalescing with existing rules
where appropriate.  Reorganize the rules and try to
annotate the reason for the different rules.

Change-Id: I2d07e7c276a9c29677f67db0ebecfc537c084965
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>