new travis build

- do pep8 and pyflakes checks
- do not tests examples with dependencies (psycopg2_pool.py, web.py, geventsendfile.py)
- do check -dbg build
- install cython from ppa
- add python 3.3

new make commands:
 - make whitespace
 - make pep8
 - make pyflakes
 - make lint       # runs all of the above
 - make travis     # runs on travis

The linters are run first to abort broken builds early.