(PP-153) Ensure SecureRandom.uuid is available

Ruby's stdlib includes SecureRandom.  In 1.9.3 SecureRandom
includes a uuid method, which is essentially a convenience
wrapper around the base random number generation.  1.8.7 did not
provide the uuid method, so this change monkey patches 1.8 to add
the uuid method (copy-paste of the code from 1.9.3).  This change
also adds tests to verify that there is a uuid method and that it
returns a properly formatted uuid string.