delfater: ensure that parent body is always closed

 * Fixes a bug where body is not enumerated (i.e. HEAD), and as such is never
   closed.
 * Users suffering from the above bug are encouraged to investigate their
   middleware order.
 * Supersedes and closes #531.

Conflicts:
	lib/rack/deflater.rb

Cherry-picked from 7bda8d485b38403bf07f43793d37b66b7a8281d6
Fix race in deflater, remove early close
fix typos

Conflicts:
	lib/rack/deflater.rb

Cherry-picked from 3ee561469dd61cc7776af4eeb06b97dcbf98f39b