Fix SSL detection.

SSL detection is broken in 7.19.3 on some systems, because curl-config --libs doesn't display all depended libraries (e.g. ssl) in all cases, see REQUIRE_LIB_DEPS in https://github.com/bagder/curl/blob/master/curl-config.in.

So, for SSL detection curl-config --libs --static-libs should be used. Also, HAVE_CURL_SSL should be defined only when one of the SSL libraries is detected, because:

"libcurl was compiled with SSL support, but configure could not determine which library was used; thus no SSL crypto locking callbacks will be set, which may cause random crashes on SSL requests"

i.e. in most cases you get library which doesn't work with SSL requests.