add OPT_HTTPAUTH flags and new OPT_SSLVERSION flags

[schnoddelbotz]

The patch allows talking to Intel vPro / AMT using go-curl. AMT requires HTTP digest auth and uses aged TLSv1, which can (and must) be explicitly specified in more recent versions of curl. Tested on macOS Sierra (which hasn't curl 7.52.0 yet but 7.49.1 -- thus I still left TLSv1_3 commented out...).
Thanks a lot for go-curl!

[schnoddelbotz]

Hmm. Sorry for the broken travis-ci build... but it's using Ubuntu Precise (12.04 LTS), which will be EOL'ed April next year. Even Debian jessie/stable has curl 7.38... Should I come back next year? ;-)

[andelf]

👍 Thanks for your work.

Take a look at compat.h
And also misc/compatgen.py

Waiting for your fix! :)

[andelf]

Update:

the compatgen.py needs an up-to-date curl repo, and all version tags.
it run through all supported versions and generate a compat.h for missing definition.

[andelf]

You see my last run of compatgen.py is curl-7_36_0. which is too old.

[andelf]

@schnoddelbotz I'll fix this.