Use the last value from the []string params instead of the first

This allow for getting the value sent from the last html element, which
is specially useful when dealing with checkboxes, when you want to
submit a value for when it's unchecked.

	<input name="foo" type="hidden" value="0">
	<input name="foo" type="checkbox" value="1">
Merge remote-tracking branch 'gorilla/master'
Merge branch 'master' of git://github.com/gorilla/schema
Add test for multiple values for non array fields
Merge pull request #7 from divoxx/master

Use last item from array when mapping to a non array/slice