Restore openssl and libscrypt includes in test_crypto_slow.c

This reverts part of commit 706c44a6ce.

It was a mistake to remove these includes: they were needed on
systems where we have openssl 1.1.0 *and* libscrypt, and where we
were validating the one against the other.

Fixes bug 22892; bugfix on 0.3.1.1-alpha.

changes/bug22892

@@ -0,0 +1,4 @@
+  o Minor bugfixes (compilation):
+    - Compile correctly when both openssl 1.1.0 and libscrypt are detected.
+      Previously this would cause an error. Fixes bug 22892; bugfix on 
+      0.3.1.1-alpha.

src/test/test_crypto_slow.c

@@ -12,8 +12,11 @@
 
 #if defined(HAVE_LIBSCRYPT_H) && defined(HAVE_LIBSCRYPT_SCRYPT)
 #define HAVE_LIBSCRYPT
+#include <libscrypt.h>
 #endif
 
+#include <openssl/evp.h>
+
 /** Run unit tests for our secret-to-key passphrase hashing functionality. */
 static void
 test_crypto_s2k_rfc2440(void *arg)