Add Travis CI configuration.

Squashed commit of the following:

commit e09e93759459c29bb28a271b98d00a9b1b999dfa
Merge: 91a4f4f aeeb2d5
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 12:39:32 2014 +0200

    Conflict resolution.

commit 91a4f4f034da964cf3d151bfeaf896dfdc78b7c9
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 11:22:30 2014 +0200

    We actually don't support Ruby 1.9

commit 649c99613791c16259366ecc65d6cde270852649
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 11:21:52 2014 +0200

    Revert "This seems to confuse Ruby 1.9"

    This reverts commit 40dc29f4d50b1f06e16f187ac33bcd1cde44c2f8.

commit 514a2698a9468a89dcb436fd1bfd2df8094442a3
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 11:21:32 2014 +0200

    Revert "Still confuses Ruby 1.9, because I fixed it wrong."

    This reverts commit 0d104891ac2839edc433de9c68b884b2f42dbce0.

commit 5ef537ebf1cedd743670c2d57923cfc182f7893a
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 11:01:12 2014 +0200

    As no one is using those reports...

commit 0d104891ac2839edc433de9c68b884b2f42dbce0
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 10:51:02 2014 +0200

    Still confuses Ruby 1.9, because I fixed it wrong.

commit 40dc29f4d50b1f06e16f187ac33bcd1cde44c2f8
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 10:34:15 2014 +0200

    This seems to confuse Ruby 1.9

commit 4302ac5e2f697ab3fba163eef13e3ba927e198f6
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 10:33:19 2014 +0200

    Make sure tmp is no longer ignored.

commit 77fda56d3af0212bdfe3b0ea205ecc0596649fe2
Author: Ramón Cahenzli <rca@psy-q.ch>
Date:   Tue May 6 10:33:12 2014 +0200

    Make sure tmp exists once and for all.