travis-ci integration (pull-tester replacement)

See the doc/travis.txt for a description of what travis is and how it works.

This is an initial descriptor to get things going. It can be changed around at any time, so discussions about what build configs to use, notifications, etc, can all take place in the form of pull-requests in the future.

At the moment, each pull-request will kick off 7 builds:
- linux x86_64 full
- linux x86_64 minimal
- linux i686 full
- linux arm no-qt
- osx x86_64 full
- win x86_64 full
- win i686 full

Build results will be similar to this: https://travis-ci.org/coryfields/bitcoin/builds/33137850 .

There are lots of features and bells/whistles to play with down the road, see [notifications](http://docs.travis-ci.com/user/notifications/) for an example.

There's also a quick build change in here to make osx build logs actually useful.
All .o files in my local installation together is a multiple of 100M already. Does it help at all if it can't even cache one full build's results?