Undo unapproved commit that removed DJGPP and WATT32

DJGPP is no longer a supported platform.  Remove all #ifdef, etc.,
cases that refer to it.  DJGPP also #define'd WATT32, so that
is now removed as well.

Based on an original patch by Neitrino Photonov <neitrinoph@gmail.com>

PR#3439

PR: 3327

Submitted by: Roumen Petrov

Windows 8 SDKs complain that GetVersion() is deprecated.

We only use GetVersion like this:

	(GetVersion() < 0x80000000)

which checks if the Windows version is NT based. Use a macro check_winnt()
which uses GetVersion() on older SDK versions and true otherwise.

Add the extension parser in the s_client, ocsp and x509 apps.

PR: 2809

DTLS/SCTP requires DATA and FORWARD-TSN chunks to be protected with
SCTP-AUTH.  It is checked if this has been activated successfully for
the local and remote peer. Due to a bug, however, the
gauth_number_of_chunks field of the authchunks struct is missing on
FreeBSD, and was therefore not considered in the OpenSSL implementation.
This patch sets the corresponding pointer for the check correctly
whether or not this bug is present.
(cherry picked from commit f596e3c491035fe80db5fc0c3ff6b647662b0003)

Submitted by: Pierre Delaage

contemporary SDK.

PR: 2830
Submitted by: Robin Seggelmann

PR: 2791
Submitted by: Ben Noordhuis

PR: 2790
Submitted by: Alexei Khlebnikov

Submitted by: Robin Seggelmann <seggelmann@fh-muenster.de>

Reduce MTU after failed transmissions.

Submitted by: Arpadffy Zoltan <Zoltan.Arpadffy@scientificgames.se>

VMS fixes: disable SCTP by default.

Submitted by: Robin Seggelmann <seggelmann@fh-muenster.de>
Reviewed by: steve

Add SCTP support for DTLS (RFC 6083).

Submitted by: Adam Langley
Reviewed by: Bodo Moeller

Submitted by: "Mauro H. Leggieri" <mxmauro@caiman.com.ar>
Reviewed by: steve

Stop warnings if OPENSSL_NO_DGRAM is defined.

Submitted by: Robin Seggelmann <seggelmann@fh-muenster.de>
Reviewed by: steve

Fix DTLS socket error bug

Submitted by: Robin Seggelmann <seggelmann@fh-muenster.de>
Reviewed by: steve

Fix BIO_accept so it can be bound to IPv4 or IPv6 sockets consistently.

submitted by Steven M. Schweda <sms@antinode.info>

Submitted by: Michael Bergandi <mbergandi@gmail.com>
Reviewed by: steve

Fix typo in crypto/bio/bss_dgram.c

PR: 2382

e_os2.h, this should fix WIN32 compilation issues and hopefully avoid
conflicts with other headers which may workaround ssize_t in different ways.

Remove useless num = 0 assignment.

Remove redundant cases on sock_ctrl(): default case handles them.