The bzip2 block size is a multiple of 100*1000 not 100*1024.
Thus, the bzip2 decoder would incorrectly decode files with larger
block sizes when it should have otherwise failed.
Fortunately, we can correct this in a backwards compatible way since
Go has no implementation of a bzip2 encoder to produce bad blocks :)

To confirm that the C bzip2 utlity chokes on this data:
	$ echo "425a683131415926535936dc55330063ffc0006000200020a40830008b00
	08b8bb9229c28481b6e2a998" | xxd -r -p | bzip2 -d

	bzip2: Data integrity error when decompressing.

Fixes #13941

Change-Id: I2402e8829a8027ef94dd4fac050b200440a3d4e4
Reviewed-on: https://go-review.googlesource.com/20011
Run-TryBot: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>