polishing
Fix typo
Switch to full gradle version
Fix potential NPE

This commit fixes a potential NPE when determining the priority of a
bean instance in case multiple candidates exist and no bean was marked
as @Primary

Issue: SPR-12024
Fix compiler warning
Revert ea16ce0

The latest build preview of jdk 1.8.0_20 does not exhibit the problem
anymore.

Issue: SPR-11973
Autowiring rejects self references to a factory method on the same bean as well

Issue: SPR-12018
TypeDescriptor's getResolvableType() and getSource() are @since 4.0
Self reference detection defensively handles null bean names

Issue: SPR-12018