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.

table t : {A : int, B : string}

task initialize = fn () => dml (UPDATE t SET A = A + 1 WHERE TRUE);
                     dml (UPDATE t SET B = 'q' WHERE TRUE)