Refine sepolicy-analyze -D / dup detection.

We were incorrectly reporting overlapping rules as duplicates.
Only report cases where an attribute-based rule is a superset
of type-based rule.  Also omit self rules as they are often due
to expansion of domain self rules by checkpolicy.

Change-Id: I27f33cdf9467be5fdb6ce148aa0006d407291833
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>