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 f [r] [[Id, Foo] ~ r] (x : $(map (fn ts => $ts) r ++ [Id = int, Foo = string]))
    : $(map (fn ts => $ts) r ++ [Foo = string]) = x

val r = {}
val x : $(map (fn ts => $ts) _ ++ [Foo = string]) = f r