Remove Fortuna generator, fix Android SecureRandom bug
This branch removes the Fortuna generator and the CombinedSecureRandom that mixes Fortuna's output with the output of the JVM's default SecureRandom implementation. Instead, it installs a single strong SecureRandom implementation.
On Linux and Android, the SecureRandom implementation reads from /dev/urandom. This avoids any weaknesses in the JVM's default SecureRandom implementation, such as CVE-2013-7372.
This branch provides further protection against CVE-2013-7372 on Android by properly seeding the OpenSSL PRNG, in case any libraries use the OpenSSL PRNG directly rather than via SecureRandom.
Closes #914 (closed)