Expose PGPSecretKeyRing constructor

The PGPSecretKeyRing is in its essence a simple enough wrapper around a
list of PGPSecretKeys. It can however only be instantiated from a binary
representation, a PGPKeyRingGenerator or bootstrapped by modifying an
existing SecretKeyRing. This is comonly fine ensure constraints from the
constructor are preserved -- but we need the access in OpenKeychain
because we just work on that low level.

Hrum.

pg/src/main/java/org/spongycastle/openpgp/PGPSecretKeyRing.java

@@ -36,7 +36,7 @@ public class PGPSecretKeyRing
     List keys;
     List extraPubKeys;
 
-    PGPSecretKeyRing(List keys)
+    public PGPSecretKeyRing(List keys)
     {
         this(keys, new ArrayList());
     }