Avoid a costly buffer-to-string operation. Instead, allocate a new
buffer, copy the chunk header and data into it and send that.

The speed difference is negligible on small payloads but it really
shines with larger (10+ kB) chunks. benchmark/http/end-vs-write-end
with 64 kB chunks gives 45-50% higher throughput. With 1 MB chunks,
the difference is a staggering 590%.

Of course, YMMV will vary with real workloads and networks but this
commit should have a positive impact on CPU and memory consumption.

Big kudos to Wyatt Preul (@wpreul) for reporting the issue and providing
the initial patch.

Fixes #5941 and #5944.

Before this commit, events were set to undefined rather than deleted
from the EventEmitter's backing dictionary for performance reasons:
`delete obj.key` causes a transition of the dictionary's hidden class
and that can be costly.

Unfortunately, that introduces a memory leak when many events are added
and then removed again. The strings containing the event names are never
reclaimed by the garbage collector because they remain part of the
dictionary.

That's why this commit makes EventEmitter delete events again. This
effectively reverts commit 0397223.

Fixes #5970.

* Run the garbage collector before creating the big array. It doesn't
  matter now but if in the future something in node.js core creates
  a lot of reclaimable garbage, that will break the test's expectation.

* The first RSS check was being done too late. The garbage collector
  might have run before the check, throwing off the 'reclaimed memory'
  calculation.

* Due to changes in how V8 represents the big array internally, the
  actual memory usage is just below 256 MB on x64. Update the test's
  expectation.

Run the garbage collector before running the actual test. It doesn't
matter now but if in the future something in node.js core creates a lot
of reclaimable garbage, that will break the test's expectation.

Flags and modes aren't the same, symlinks are followed in all of the
path but the last component, docs should say something about what the
mode argument is for and when its used, fs.openSync should point to the
function that contains the docs for its args, as fs.writeSync does.

Adds the documentation requested in #5017.

Quoting the CVE:

    Google V8, as used in Google Chrome before 28.0.1500.95, allows
    remote attackers to cause a denial of service or possibly have
    unspecified other impact via vectors that leverage "type confusion."

Likely has zero impact on node.js because it only runs local, trusted
code but let's apply it anyway.

This is a back-port of upstream commit r15665. Original commit log:

    Use internal array as API function cache.

    R=yangguo@chromium.org
    BUG=chromium:260106
    TEST=cctest/test-api/Regress260106

    Review URL: https://codereview.chromium.org/19159003

Fixes #5973.

If an error listener is added to a stream using once() before it is
piped, it is invoked and removed during pipe() but before pipe() sees it
which causes it to be emitted again.

Fixes #4155 #4978

Conflicts:
	deps/v8/test/cctest/test-api.cc
	lib/events.js
	lib/http.js