doc: improve example of process.hrtime()

The example clarifies now that diff[0] * 1000000000 + diff[1] equals
the result in nanoseconds.
node: move symbol caching to Load()
child_process: don't `resume()` created socket

Calling `resume()` on a stream switches it to the old mode which causes
piping stdio from a child process to fail.

Fixes joyent/node#4510.
stream: Clean up more effectively in pipe()
child_process: Pull through untouched stdio streams

Otherwise child procs will never emit a 'close' event if you don't
ever consume their streams, because they will never hit the EOF.
src: make node_isolate global

V8 3.15 has new API functions that let you specify the Isolate. V8 and
node.js generally spend 0.5-3.5% of the time in pthread_getspecific(),
looking up the current Isolate. Avoid that overhead by making "our"
isolate global so we can pass it around. The change to the new API is
introduced in follow-up commits.
src: pass node_isolate to String::Empty
src: pass node_isolate to Integer::New
src: pass node_isolate to Local<>::New
src: pass node_isolate to True() and False()
src: pass node_isolate to Null()
src: pass node_isolate to Undefined()
dtrace: SeqAsciiString was renamed to SeqOneByteString in v8
dtrace: fix style in ustack helper
dtrace: x64 ustack helper
dtrace: Make D style more D-ish
dtrace: More style

Continuation lines should be indented with 4 spaces, not a tab.
build: fail w/err msg when missing binutils

Building --with-dtrace requires objdump from GNU binutils.
This change inserts a helpful error message if there is a
problem executing objdump.
dgram: don't assert on send('string')

Raise a TypeError when the argument to send() or sendto() is anything
but a Buffer.

Fixes the following assertion:

  $ node -e 'require("dgram").createSocket("udp4").send("BAM")'
  node: ../../src/udp_wrap.cc:220: static v8::Handle<v8::Value>
  node::UDPWrap::DoSend(const v8::Arguments&, int): Assertion
  `Buffer::HasInstance(args[0])' failed.
  Aborted (core dumped)

Fixes #4496.
net: fix bufferSize include writableStream length

socket.bufferSize missed to include the length of internal buffers in
writableStream.