TLS-SRP: support added when using GnuTLS

configure.ac

include/curl/curl.h

lib/gtls.c

lib/strerror.c

lib/url.c

lib/urldata.h

lib/version.c

src/main.c

tests/FILEFORMAT

tests/certs/srp-verifier-conf

tests/certs/srp-verifier-db

tests/data/Makefile.am

tests/data/test320

tests/data/test321

tests/data/test322

tests/data/test323

tests/data/test324

tests/runtests.pl

tests/serverhelp.pm

tests/sshhelp.pm