Fix attribute check for gnutls

As of version 3.6.6 gnutls checks to see if we have the CKA_SIGN and
CKA_DECRYPT attributes set for PSS signing and OAEP decryption keys.
These are set in the cache but not processed by our attribute handling
code, so add them.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/pkcs11.c b/pkcs11.c
index 123d4a6..6311e3a 100644
--- a/pkcs11.c
+++ b/pkcs11.c
@@ -318,6 +318,8 @@
 		Xb(CKA_VERIFY_RECOVER);
 		Xb(CKA_DERIVE);
 		Xb(CKA_PRIVATE);
+		Xb(CKA_SIGN);
+		Xb(CKA_DECRYPT);
 	default:
 		attr->ulValueLen = 0;
 		break;