Bzip2::Write mutates payload - critical!

[maasha]

Consider the test dataset from issue #22:

bunzip2 the test dataset
bzip2 the test dataset with Bzip2::Write in test1.bz2
bzip2 the test dataset with command line bzip2 in test2.bz2

Notice the huge size difference between test1.bz2 and test2.bz2
Notice that bzcat test1.bz2 | md5sum differs from bzcat test2.bz2 | md5sum

Versions:
Linux orsted 3.2.0-4-amd64 #1 SMP Debian 3.2.46-1 x86_64 GNU/Linux
bzip2, a block-sorting file compressor. Version 1.0.6, 6-Sept-2010.
bzip2-ruby (0.2.7)