http: force socket encoding to be null

Otherwise the string triggers an assertion error in node_http_parser.c,
line 370:

    assert(Buffer::HasInstance(args[0]) == true);

because the first argument is not a Buffer object.
crypto: try moving read head in Peek()

Otherwise it might get stall (`Peek()` will return zero-length chunk)
in following situation:

1. `Write(kBufferLength)`
2. `Read(kBufferLength)`
3. `Write(anything)`
4. `Peek()` => `len=0`
crypto: unbreak build with no-NPN shared openssl

Unbreak the build when linking against a shared version of OpenSSL that
doesn't support NPN (Next Protocol Negotiation.)

Fixes the following build error:

  ../src/node_crypto.cc:140: error: no member function
  'AdvertiseNextProtoCallback' declared in
  'node::crypto::SSLWrap<node::TLSCallbacks>'
  ../src/node_crypto.cc:147: error: no member function
  'SelectNextProtoCallback' declared in
  'node::crypto::SSLWrap<node::TLSCallbacks>'
src: remove container_of, use CONTAINER_OF

CONTAINER_OF was introduced a while ago but was not used consistently
everywhere yet.  This commit fixes that.

Why CONTAINER_OF instead of container_of?  The former makes it crystal
clear that it's a macro, not a function.
build: make v8 use random seed for hash tables

Upstream V8 as of commit v8/v8@4bc70e8 uses a fixed seed of 314159265
for hash tables unless instructed otherwise.  Tell V8 to keep using a
random seed.
process: add process._heapInfo() method

Binding to v8::V8::GetHeapStatistics() to help with core debugging.

Might also be useful for profiling and monitoring tools but keep in
mind, dear reader, that the underscore in the method name means it's
not part of the official API.

Fixes #6414.
src: track gc times wip

Works but needs some deliberation on whether a) we actually want this,
and b) what direction it should take.

Refs #6414.
src: add gc statistics

TODOs:

* multi-context support should take care not to clobber the queue
* figure out the best way to call into JS land
* uncruft-ify code, it's not very elegant now