Add the possibility to build without the ENGINE framework.

PR: 287

crypto/dsa/dsa.h

@@ -135,8 +135,10 @@ struct dsa_st
 	int references;
 	CRYPTO_EX_DATA ex_data;
 	const DSA_METHOD *meth;
+#ifndef OPENSSL_NO_ENGINE
 	/* functional reference if 'meth' is ENGINE-provided */
 	ENGINE *engine;
+#endif
 	};
 
 #define DSAparams_dup(x) (DSA *)ASN1_dup((int (*)())i2d_DSAparams, \