SpeechSynthesis: test for and prevent duplicate voice entries

android/eSpeakTests/src/com/reecedunn/espeak/test/SpeechSynthesisTest.java

             final SpeechSynthesis synth = new SpeechSynthesis(getContext(), mCallback);
             mVoices = new HashMap<String, Voice>();
             for (Voice voice : synth.getAvailableVoices()) {
+                assertThat(mVoices.get(voice.name), is(nullValue()));
                 mVoices.put(voice.name, voice);
             }
             assertThat(mVoices, is(notNullValue()));

android/src/com/reecedunn/espeak/SpeechSynthesis.java

             if (name.equals("fa-pin")) {
                 // Android locales do not support scripts, so fa-Latn is not possible for Farsi Pinglish:
                 locale = null;
+            } else if (identifier.equals("asia/fa-en-us")) {
+                locale = null;
             } else if (name.equals("om")) {
                 // This is an experimental voice that is not currently well tested to be used.
                 locale = null;