Normalize to absolute paths so that patterns work as expected.

This solves a problem where configuration treats dirname and ./dirname (and ./dirname and ././dirname, etc) as non-equivilant values, leading to unexpected bahvior when patterns are not consistently expressed. For example, given the pattern "spec/models/*_spec.rb" and an exclude_pattern "./spec/models/*", nothing would be excluded because of the spec ./spec mismatch.