Update to latest version of libtextsecure for simplified interface.

1) Switch to new TextSecureAddress addressing, rather than mixing
   long-based recipient IDs into libtextsecure.

2) Get rid of RecipientFormattingException throws in calls to
   RecipientFactory.

Closes #2570

src/org/thoughtcrime/securesms/crypto/SessionUtil.java

@@ -0,0 +1,24 @@
+package org.thoughtcrime.securesms.crypto;
+
+import android.content.Context;
+import android.support.annotation.NonNull;
+
+import org.thoughtcrime.securesms.crypto.storage.TextSecureSessionStore;
+import org.thoughtcrime.securesms.recipients.Recipient;
+import org.whispersystems.libaxolotl.AxolotlAddress;
+import org.whispersystems.libaxolotl.state.SessionStore;
+import org.whispersystems.textsecure.api.push.TextSecureAddress;
+
+public class SessionUtil {
+
+  public static boolean hasSession(Context context, MasterSecret masterSecret, Recipient recipient) {
+    return hasSession(context, masterSecret, recipient.getNumber());
+  }
+
+  public static boolean hasSession(Context context, MasterSecret masterSecret, @NonNull String number) {
+    SessionStore   sessionStore   = new TextSecureSessionStore(context, masterSecret);
+    AxolotlAddress axolotlAddress = new AxolotlAddress(number, TextSecureAddress.DEFAULT_DEVICE_ID);
+
+    return sessionStore.containsSession(axolotlAddress);
+  }
+}