polarssl: provide a (weak) random function

This now provides a weak random function since PolarSSL doesn't have a
quick and easy way to provide a good one. It does however provide the
framework to make one so it _can_ and _should_ be done...
vtls: repair build without TLS support

... by defining Curl_ssl_random() properly
smtp: fixed a segfault during test 1320 torture test

Under these circumstances, the connection hasn't been fully established
and smtp_connect hasn't been called, yet smtp_done still calls the state
machine which dereferences the NULL conn pointer in struct pingpong.
opts: fixed some typos
cyassl: use RNG_GenerateBlock to generate a good random number
cyassl: fix the test for ASN_NO_SIGNER_E

It's an enum so a macro test won't work. The CyaSSL changelog doesn't
say exactly when this error code was introduced, but it's likely
to be 2.7.0.
axtls: define curlssl_random using axTLS's PRNG
ssl: generalize how the ssl backend identifier is set

Each backend now defines CURL_SSL_BACKEND accordingly. Added the *AXTLS
one which was missing previously.
curl_version_info.3: 'ssl_version_num' is always 0

... and has been so since 2005
schannel: use CryptGenRandom for random numbers

This function is available for every Windows version since Windows 95/NT.

reference:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa379942.aspx
CURLOPT_HEADEROPT.3: typo: do -> to
RELEASE-NOTES: synced with 7bb4c8cadb5d0
openssl: make ossl_send return CURLE_OK better

Previously it only returned a CURLcode for errors, which is when it
returns a different size than what was passed in to it.

The http2 code only checked the curlcode and thus failed.
FEATURES: minor update
CURLOPT_SSL_VERIFYPEER.3. add a warning about disabling it
HTTP2: Support expect: 100-continue

"Expect: 100-continue", which was once deprecated in HTTP/2, is now
resurrected in HTTP/2 draft 14.  This change adds its support to
HTTP/2 code.  This change also includes stricter header field
checking.
ssl: provide Curl_ssl_backend even if no SSL library is available
gtls: only define Curl_gtls_seed if Nettle is not being used
HTTP/2: Fix infinite loop in readwrite_data()

To prevent infinite loop in readwrite_data() function when stream is
reset before any response body comes, reset closed flag to false once
it is evaluated to true.
Curl_ossl_version: detect and show libressl

LibreSSL is otherwise OpenSSL API compliant (so far)