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.

type r = {A : int, B : int, C : float}
type string = int

val x : r = {A = 1, B = "hi", C = 2.3}