curl_global_cleanup(). Update corresponding man pages...
Improve the logic in curl_global_cleanup() and curl_global_init() so that
they are not called twice if the application libraries have been
initialized and make sure to reset the init flags in curl_global_cleanup().
it will make it better when the application uses several libs that use
openssl and it also enables us to do the win32 winsock initing in the future
if we want to
