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/
http: Fix overlooked agent.globalAgent export

Noticed by @bnoordhuis in https://github.com/joyent/node/pull/5991#discussion_r5575946
https: fix default port

https.get('https://github.com/') should use port 443, not 80.
test: Move test-http-default-port from disabled to simple
build: embed the mdb_v8.so into the binary

This builds and includes the mdb_v8.so in the binary of node so mdb
can be sure to always use the latest version
build: fix ia32 sunos, elfwrap only needs -64
doc: add a missing word in streams doc

Ignore encoding *if* chunk is a buffer
repl: Add 'smalloc' to list of known modules
tls_wrap: DRY ClientHelloParser

Share ClientHelloParser code between `tls_wrap.cc` and `node_crypto.cc`.

fix #5959
tls: asynchronous SNICallback

Make ClientHelloParser handle SNI extension, and extend `_tls_wrap.js`
to support loading SNI Context from both hello, and resumed session.

fix #5967
crypto: fix signed/unsigned comparison warning

The type of the expression `(uint16_t) server_names_len + 2` gets
implicitly widened to int. Change the type of server_names_len to
uint32_t to avoid the following warnings:

    ../../src/node_crypto_clienthello.cc:144: warning: comparison
    between signed and unsigned integer expressions
    ../../src/node_crypto_clienthello.cc:146: warning: comparison
    between signed and unsigned integer expressions
src: fix WITH_GENERIC_STREAM() type check bug

The handle object was checked against the wrong constructor template.
Put another way, it was unwrapped as the wrong StreamWrap type.
multi-context wip