docs: Warning about consuming response
http: improve chunked res.write(buf) performance

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.
events: fix memory leak, don't leak event names

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.
test: fix pummel/test-net-connect-memleak

* 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.
test: future-proof simple/test-event-emitter-memory-leak

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.
build: fix --without-ssl build

Build breakage accidentally introduced in 8e29ce9 during code cleanup.

HAVE_OPENSSL is always defined (as either 0 or 1) so use #if rather
than #ifdef.

Fixes #5979.
util: add isPrimitive check
smalloc: fix assertion fails/segfault

* Numeric values passed to alloc were converted to int32, not uint32
  before the range check, which allows wrap around on ToUint32. This
  would cause massive malloc calls and v8 fatal errors.
* dispose would not check if value was an Object, causing segfault if a
  Primitive was passed.
* kMaxLength was not enumerable.
smalloc: remove double checks

Now that values are checks in JS, no need for them to be checked in C++.
src: remove non-isolate PersistentToLocal()

There is no need for it and it's a tiny bit slower than the version of
PersistentToLocal() that takes a v8::Isolate* as its first argument.
process: set key properties as ReadOnly
npm: Upgrade to 1.3.7
src: remove non-isolate PersistentToLocal(), v2

Commit 78d9094 updated src/*.cc to use the version of PersistentToLocal
that takes a v8::Isolate* as its first argument. This commit removes
the non-isolate version.
crypto: fix another over-run in bio

When doing `FreeEmpty`, `NodeBIO` skips pre-allocated `head_` buffer.
However this might lead to double-freeing buffers since in `~NodeBIO()`
we're starting deallocation from `head_` buffer.
src: use PersistentToLocal() in a few more places

Update a few more `Local<T>::New(isolate, persistent)` call sites to
`PersistentToLocal(isolate, persistent)` - the latter has a fast path
for non-weak persistent references.
src: use static_cast for void-to-T casts

Code cleanup, replace a few uses of reinterpret_cast<T*>(void_ptr) with
static_cast<T*>(void_ptr).
tls: fix handling of `SNICallback` server option

It shouldn't ignore it!

There're two possibile cases, which should be handled properly:

1. Having a default `SNICallback` which is using contexts, added with
  `server.addContext(...)` routine
2. Having a custom `SNICallback`.

In first case we may want to opt-out setting `.onsniselect` method (and
thus save some CPU time), if there're no contexts added. But, if custom
`SNICallback` is used, `.onsniselect` should always be set, because
server contexts don't affect it.
v8: fix openbsd build

This is [1] applied ahead of time. Summary:

    OpenBSD doesn't have <ucontext.h>. ucontext_t lives in <signal.h>
    and is a typedef for struct sigcontext. There is no uc_mcontext.

[1] https://codereview.chromium.org/21705003/
doc: fs.open, fix flag/mode confusion, etc.

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.
doc: document domain.enter() and domain.exit()

Adds the documentation requested in #5017.