Spring cleanup

This does some spring cleaning on Utilrb
 - remove some deprecated /barely working / totally unused code
 - remove 1.8 compatibility code
 - port to minitest. Ruby is bundling minitest as the test library, with a "shim" to make it compatible with Test::Unit. Unfortunately, this shim is broken if the minitest gem gets installed. The most robust option is to simply use Minitest directly.
 - remove warnings issued by -w (not all warnings are fixed, only the most straightforward ones)