buffer: fix Buffer::Copy regression from 00b4b7b

If the end argument is omitted or not a number, make it default to
the end of the buffer, not zero.

Ideally, it should not matter what it defaults to because the JS shim
in lib/buffer.js should handle that but there are still several places
in node.js core that secrete SlowBuffers, hence Buffer::Copy() gets
called without going through Buffer.prototype.copy() first.
test: fix pummel test out-of-memory errors

Fix the following OOM error in pummel/test-net-connect-memleak
and pummel/test-tls-connect-memleak:

  FATAL ERROR: CALL_AND_RETRY_0 Allocation failed - process out of
  memory

Commit v8/v8@91afd39 increases the size of the deoptimization table
to the extent that a 64M float array pushes it over the brink. Switch
to SMIs so it stays below the limit.

pummel/test-net-connect-memleak is still failing albeit with a different
error this time. Needs further investigation.

  === release test-net-connect-memleak ===
  Path: pummel/test-net-connect-memleak
  -64 kB reclaimed
  assert.js:102
    throw new assert.AssertionError({
          ^
  AssertionError: false == true
      at done [as _onTimeout] (/home/bnoordhuis/src/nodejs/master/
  test/pummel/test-net-connect-memleak.js:48:3)
      at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
      at process._makeCallback (node.js:306:20)