Fix very predictable random data on some platforms

Misc::randCode does not generate significantly random data for Windows
platforms with a local database. This stems from the random seed using the
milliseconds from the current time of day and the database connection time,
in microseconds. Because Windows has especially poor sub-second time
resolution via the microtime() function, the seed does not have many
variations.

This patch addresses the issue by using the included Crypto::random()
function as a source of random data rather than the mt_rand() function, as
it uses native cryptographic random data generators if possible to generate
the data, and uses microtime() as a fallback if no other source of random
data is available on the platform.