check for fingerprint of any subkey (arguable?)

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/UncachedKeyRing.java

@@ -215,6 +215,17 @@ public class UncachedKeyRing {
 
     }
 
+    public boolean containsSubkey(String expectedFingerprint) {
+        Iterator<PGPPublicKey> it = mRing.getPublicKeys();
+        while (it.hasNext()) {
+            if (KeyFormattingUtils.convertFingerprintToHex(
+                    it.next().getFingerprint()).equals(expectedFingerprint)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     public interface IteratorWithIOThrow<E> {
         public boolean hasNext() throws IOException;
         public E next() throws IOException;