Revert "Revert "Revert "fix memory leaks in bz_reader_read""" ;)

This reverts commit e58f154624ff2d770e92a70e0d8fb1a9e6564720 because
the "fix" is causing double frees when piped through ruby-gpgme. See
issue #12.
This code breaks Ruby 2.1 as well as Rubinius

The Rubinius maintainer says this code isn't even needed anyway so...