PROBLEM: :legacy-mode :auto/true thawing was resulting in JVM core
dumps when attempting to use Snappy to decompress encrypted data.
CAUSE: The org.iq80.snappy implementation seems to choke on the
random IV byte data being generated by the AES128 encrypter. This
may or may not be a bug (still awaiting feedback from lib's authors).
SOLUTION: We're only susceptible to this issue when trying to
decompress data that is: a) encrypted, b) being thawed in legacy mode.
In particular, we're _not_ susceptible to this issue when thawing
in non-legacy mode because in that case we have a header explicitly
warning us that the data is encrypted.
An obvious work-around, therefore, is just to disable decryption when
attempting to thaw legacy-mode data. In practice this isn't a problem
because older versions of Nippy didn't support encryption anyway.
