Add .travis.yml for pull request checking

But notifications are disabled
Fix test runs on 1-4-stable, but they still fail

But they fail less than on master.
use minitest
more ignores
Ensure that test task builds first.
Rakefile cleanup: specify MIT license, use dependency calls, clean up spec_extras.
fix detection of rb_ary_subseq(), use mkmf's have_func()

* See tenderlove/racc#34 and 1b1942a0