Allow attribute filter to be passed on queries, use during group lookups

Fixes: #7
Fix up unit tests for new cache format
Normalize attrlist ordering, add test case for same
issues/7: Update per review feedback
Merge remote-tracking branch 'upstream/master' into issues/7
Update CONTRIBUTORS; Indeed.com agrees to the CA
Update docs, remove change to pyramid_ldap/tests from prior rev
Merge branch 'issues/7' of github.com:charles-dyfis-net/pyramid_ldap into upstream_merges

Conflicts:
	CHANGES.txt
	CONTRIBUTORS.txt
	pyramid_ldap/__init__.py