curl 4.0 "Option SOME_OPTION (10123) not supported"

[jeroen]

As of curl 4.0 we do stricter type checking based on typecheck-gcc.h. Unfortunately it looks like these macros were incomplete in old versions of libcurl.

This is particularly a problem on travis which still defaults to Ubuntu 14.04 which has libcurl 7.35.0. But also the CRAN mac builder runs El-Capitain which targets libcurl 7.43.0.

As a solution maybe we should only use strict type checking on recent enough versions of libcurl.

[jeroen]

One example is UNIX_SOCKET_PATH used by stevedore. See travis log.