require 'crack/util' in the cracker adapter

The `Crack::XML` uses `Crack::Util` https://github.com/jnunemaker/crack/blob/v0.4.2/lib/crack/xml.rb#L181.
Normally this would be required when someone does `require 'crack'` but `Fogbugz::Adapter::XML::Cracker` only has `require 'crack/xml'`.

This pull request has a change where I add a test that fails without `Crack::Util` (based on output I actually got from hosted FogBugz), and then the fix to make the tests pass.