Use correct OpenSSL thread safety macros on OS X (closes #209) Create an Autoconf test to determine if pthread_t is a pointer or scalar type, and use the appropriate CRYPTO_THREADID_set macro based on the result.

fun main () : transaction page =
    s <- source 0;
    n <- get s;
    set s (n + 1);
    n' <- get s;
    return <xml>{[n']}</xml>