Merge remote branch 'github/exceptions'

* github/exceptions:
  Shift exception formatting into the UI
  cooker: don't show a traceback for ParseError
  cooker: don't show a useless traceback for SyntaxError
  cooker: use logger.exception for config file parse errors
  cooker: pass traceback back from parsing thread
  cooker: show a useful message for ParsingFailure
  bb.exceptions: don't show a repr of 'self'
  codeparser.py: fix syntax error in exception handling
  codeparser.py: Ignore incomplete cache files
  bb.exceptions: handle tb entries without context
  bb.exceptions: add to_string convenience function
  bb.exceptions: add code to create pickleable traceback entries
  bb.namedtuple_with_abc: add useful util from activestate

diff --cc lib/bb/cooker.py
Simple merge