Expanded travis-ci support

[Igal Koshevoy]

travis-ci is an open source continuous integration system. It watches our source code to make sure the tests pass and yells at us when there's a problem. You can see the latest status at http://travis-ci.org/#!/calagator/calagator

The big change is that now we're testing against more versions of Ruby (ree, 1.8.7, 1.9.2 and 1.9.3), and each of those against the three databases that Calagator can use (sqlite3, postgresql, mysql), so there are twelve permutations of tests of a version of Ruby against a particular database. This required a variety of low-level changes to the code, although no functionality was changed.

I also tried adding support for JRuby, Rubinius and MagLev, but these have serious compatibility problems that make it unlikely for them to be able to run Calagator any time soon. It's not a problem with our code, but rather that they don't support many of the libraries we rely on. For example, they blow to pieces on multibyte strings used by Loofah, burst into flames when trying to run their API-incompatible version of Nokogiri, or fail hard on libraries that use C extensions.

-igal