clear user preferences in main activity onCreate

src/github.com/getlantern/lantern-mobile/app/src/main/java/org/getlantern/lantern/activity/LanternMainActivity.java

@@ -61,6 +61,10 @@ protected void onCreate(Bundle savedInstanceState) {
         mPrefs = Utils.getSharedPrefs(context);
 
         LanternUI = new UI(this, mPrefs);
+        // since onCreate is only called when the main activity
+        // is first created, we clear shared preferences in case
+        // Lantern was forcibly stopped during a previous run
+        LanternUI.clearPreferences();
 
         // the ACTION_SHUTDOWN intent is broadcast when the phone is
         // about to be shutdown. We register a receiver to make sure we

src/github.com/getlantern/lantern-mobile/app/src/main/java/org/getlantern/lantern/model/UI.java

@@ -396,6 +396,10 @@ public boolean useVpn() {
         return mPrefs.getBoolean(LanternConfig.PREF_USE_VPN, false);
     }
 
+    public void clearPreferences() {
+        mPrefs.edit().putBoolean(LanternConfig.PREF_USE_VPN, false).commit();
+    }
+
     // update START/STOP power Lantern button
     // according to our stored preference
     public void setBtnStatus() {