Support for Signal calls.

Merge in RedPhone

// FREEBIE

src/org/thoughtcrime/redphone/audio/AudioException.java

@@ -0,0 +1,23 @@
+package org.thoughtcrime.redphone.audio;
+
+/**
+ * An exception related to the audio subsystem.
+ *
+ * @author Stuart O. Anderson
+ */
+public class AudioException extends Exception {
+  private final String clientMessage;
+
+  public AudioException(String clientMessage) {
+    this.clientMessage = clientMessage;
+  }
+
+  public AudioException(AudioException cause) {
+    super(cause);
+    this.clientMessage = cause.clientMessage;
+  }
+
+  public String getClientMessage() {
+    return clientMessage;
+  }
+}