Reduce RelationCounterField ID signal conflicts and harden tests.
Review Request #7166 — Created April 4, 2015 and submitted
RelationCounterFields were using RelationTracker instance IDs as the dipsatch_uid when listening to post_save signals, which could theoretically conflict with another object that happened to use the same numeric ID for another purpose. We now have additional information in the dispatch UID to prevent such a conflict. The unit tests have also been hardened for the case where there's already legitimate signal connections to the post_save signal.
Unit tests pass.
Tool: Pyflakes Processed Files: djblets/db/tests/test_relation_counter_field.py djblets/db/fields.py Tool: PEP8 Style Checker Processed Files: djblets/db/tests/test_relation_counter_field.py djblets/db/fields.py