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 ack (m, n) =
    if m = 0 then
        n + 1
    else if n = 0 then
        ack (m - 1, 1)
    else
        ack (m - 1, ack (m, n - 1))

fun main n = return <xml>{[ack (n, 4)]}</xml>