Weave: deprecate the module and disable slow tests on TravisCI

Deprecation: see gh-3171 and recent mailing list discussions.

TravisCI timeout issue: see any recent PR. Weave tests marked with ``@dec.slow`` will now only run if an environment variable ``RUN_WEAVE_TESTS`` is set. Runtime of full test suite improves by more than 50%.

Please don't merge until we've created https://github.com/scipy/weave/ and released a first version of that standalone package on PyPi.