More robust zk client error handling: support progressively more severe retry logic.
Automatic fork and InheritedError handling:
  Lazy reconnects reduce zookeeper and redis server load.
  Reduces/prevents kernel mutex deadlocks in forking env.
Trace connection debug logging.
Remove commented out code.  Add compat note.
Fix existing tests.
trace_id test.
Cleanup
Add vendor/ to gitignore
Tests for redis command dispatch failure handling.
Cleanup some spec cruft.
Merge branch 'connection-handling-improvements'