Use the Fortuna generator instead of the JVM's SecureRandom. Bug #4.

Note that this is only the generator part of Fortuna, not the
accumulator. The generator requires a seed, which is provided by a
platform-specific implementation of SeedProvider. On Linux the
implementation reads the seed from /dev/urandom.

briar-tests/src/org/briarproject/TestSeedProvider.java

@@ -0,0 +1,16 @@
+package org.briarproject;
+
+import java.util.Random;
+
+import org.briarproject.api.crypto.SeedProvider;
+
+public class TestSeedProvider implements SeedProvider {
+
+	private final Random random = new Random();
+
+	public byte[] getSeed() {
+		byte[] seed = new byte[32];
+		random.nextBytes(seed);
+		return seed;
+	}
+}