Fix #438 Avoid DDOS attacks

app/lib/constants.js

app/lib/streams/bma.js

app/lib/system/limiter.js

app/lib/system/network.js

test/fast/limiter-test.js

test/integration/forwarding.js

test/integration/identity-test.js

test/integration/revocation-test.js

test/integration/tests.js

test/integration/transactions-test.js