updated to rails 3

Conflicts:
	lib/slug/slug.rb
updated to rails 3

Conflicts:
	lib/slug/slug.rb
updated to rails 3
touchup after merge from dwillis-master
fixed inconsistency in docs
added rails version check
added another test case
Applying Rob's fix
bumped version and updated active_support dependency

Conflicts:
	slug.gemspec
note re: Rails 3 compatibility
added contrib line for willis
Some tweaks