Add the possibility to build without the ENGINE framework.

PR: 287

crypto/rsa/rsa_test.c

@@ -16,7 +16,9 @@ int main(int argc, char *argv[])
 }
 #else
 #include <openssl/rsa.h>
+#ifndef OPENSSL_NO_ENGINE
 #include <openssl/engine.h>
+#endif
 
 #define SetKey \
   key->n = BN_bin2bn(n, sizeof(n)-1, key->n); \