Replace glob with explicit requires.

The Selenium project has a JRuby-based build, and we package our gem dependencies as `jar` files.

The usage of `Dir.glob` to dynamically require files doesn't seem to work well with this setup - we get errors like ` undefined method 'csc'` since the files were never required. 

Changing this to explicit requires work fine, since the files are still available on the `$LOAD_PATH`. This patch makes sure we can package the gem as a jar file and have things work as expected.