Run integration tests on MySQL (with empty database) in TravisCI

[php-coder]

Add new profile travis that will use MySQL and start with empty database.

Useful links:

• http://docs.travis-ci.com/user/database-setup/
• http://docs.travis-ci.com/user/environment-variables/#Default-Environment-Variables (for activating travis profile)

[php-coder]

Also it should be documented on wiki (see #257)