Fixed AddAttachments extension method

Rewriten AddAttachments extension method so it does not throw an exception (pasted below) when passing List to intent.PutExtra...

    10-16 23:20:17.596 W/Bundle  (20747): Key android.intent.extra.STREAM expected Parcelable but value was a java.util.ArrayList.  The default value <null> was returned.
    10-16 23:20:17.596 W/Bundle  (20747): Attempt to cast generated internal exception:
    10-16 23:20:17.596 W/Bundle  (20747): java.lang.ClassCastException: java.util.ArrayList cannot be cast to android.os.Parcelable
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.os.Bundle.getParcelable(Bundle.java:1179)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.content.Intent.getParcelableExtra(Intent.java:4330)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.content.Intent.migrateExtraStreamToClipData(Intent.java:6855)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.app.Instrumentation.execStartActivity(Instrumentation.java:1411)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.app.ContextImpl.startActivity(ContextImpl.java:957)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.app.ContextImpl.startActivity(ContextImpl.java:939)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.content.ContextWrapper.startActivity(ContextWrapper.java:284)
    10-16 23:20:17.596 W/Bundle  (20747): 	at mono.java.lang.RunnableImplementor.n_run(Native Method)
    10-16 23:20:17.596 W/Bundle  (20747): 	at mono.java.lang.RunnableImplementor.run(RunnableImplementor.java:29)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.os.Handler.handleCallback(Handler.java:725)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.os.Handler.dispatchMessage(Handler.java:92)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.os.Looper.loop(Looper.java:137)
    10-16 23:20:17.596 W/Bundle  (20747): 	at android.app.ActivityThread.main(ActivityThread.java:5041)
    10-16 23:20:17.596 W/Bundle  (20747): 	at java.lang.reflect.Method.invokeNative(Native Method)
    10-16 23:20:17.596 W/Bundle  (20747): 	at java.lang.reflect.Method.invoke(Method.java:511)
    10-16 23:20:17.596 W/Bundle  (20747): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    10-16 23:20:17.596 W/Bundle  (20747): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    10-16 23:20:17.596 W/Bundle  (20747): 	at dalvik.system.NativeStart.main(Native Method)