[MRG+1] Use best practices for TLS connections when using Twisted>=14.0 #1794
This is another take at the various TLS, SSL, SNI issues, assuming scrapy using Twisted 14.0+
It solved #1227 for me.
It changes the default TLSv1.0-only to SSLv23 (protocol version negotiation, "version flexible" as OpenSSL calls it)
A new setting
Also remove TLSv1.1 and TLSv1.2 method: these are available only from pyOpenSSL 0.14 https://github.com/pyca/pyopenssl/releases/tag/v0.14a1