For the remaining programs,
we define a new GODEBUG setting that
allows individual programs to opt back in to the old behavior.
A GODEBUG setting may not be added if doing so is infeasible,
but that should be extremely rare.

GODEBUG settings added for compatibility will be maintained
for a minimum of two years (four Go releases).
Some, such as `http2client` and `http2server`,
will be maintained much longer, even indefinitely.

# CL 157090043 crypto/tls: support TLS_FALLBACK_SCSV as a server., Adam Langley <******@****.***>
pkg crypto/tls, const TLS_FALLBACK_SCSV = 22016
pkg crypto/tls, const TLS_FALLBACK_SCSV uint16

# CL 107400043 crypto/tls: Added dynamic alternative to NameToCertificate map for SNI, Percy Wegmann <******@****.***>
pkg crypto/tls, type ClientHelloInfo struct
pkg crypto/tls, type ClientHelloInfo struct, CipherSuites []uint16