Make all configuration macros available for application by making

sure they are available in opensslconf.h, by giving them names starting
with "OPENSSL_" to avoid conflicts with other packages and by making
sure e_os2.h will cover all platform-specific cases together with
opensslconf.h.

I've checked fairly well that nothing breaks with this (apart from
external software that will adapt if they have used something like
NO_KRB5), but I can't guarantee it completely, so a review of this
change would be a good thing.

crypto/dsa/dsa_lib.c

@@ -257,7 +257,7 @@ void *DSA_get_ex_data(DSA *d, int idx)
 	return(CRYPTO_get_ex_data(&d->ex_data,idx));
 	}
 
-#ifndef NO_DH
+#ifndef OPENSSL_NO_DH
 DH *DSA_dup_DH(const DSA *r)
 	{
 	/* DSA has p, q, g, optional pub_key, optional priv_key.