Fix Rake.verbose to return true/false even if unset

[zenspider]

Unset returns FileUtilsExt.verbose_flag which is set to Object.new by default, which is truthy. Compare against DEFAULT and return verbose_flag only if set.

This is made extra confusing by the fact that this project uses its own TestTask which sets verbose outside of the test run... so this extends the verbose test by setting it back to DEFAULT.