Now depends on billiard 2.7.3.27
Fixes mongodb_options error.  Closes #1303
Fixes mongodb tests
Fixes mongodb backend error. Closes #1303
Travis CI: Python 2.5 no longer works due to missing ssl library, so disable CI for Py2.5
dump_body did not show message body properly when isa buffer instance
Now depends on billiard 2.7.3.28
Retry policy max_retries should be 3, not 100.  Closes #1305
Updates Changelog
Bumps version to 3.0.19
Remove outdated/uneeded files to make dist smaller
Merge branch '3.0'

Conflicts:
	Changelog
	README.rst
	celery/__init__.py
	celery/app/defaults.py
	celery/worker/consumer.py
	docs/includes/introduction.txt
	requirements/default.txt
	setup.cfg
Py3 fixes
flakes
tests passing