[TIMOB-1977] Android: Backing out of window with other thread using proxies can cause FC

If you back out of a window while a separate thread (such as a callback from an XHR, which is how we discovered this problem) is making use of proxy objects (view proxies and such) on that window, you can cause an FC. The FC can occur at multiple places in code, often in the form of a NullPointerException when trying to access something that doesn't exist anymore because the window's context and activity have been released. Here's a sample FC:

E/TiUncaughtHandler(  231): java.lang.NullPointerException
E/TiUncaughtHandler(  231):     at ti.modules.titanium.ui.TableViewProxy.rowProxyFor(TableViewProxy.java:400)
E/TiUncaughtHandler(  231):     at ti.modules.titanium.ui.TableViewProxy.handleInsertRowBefore(TableViewProxy.java:240)
E/TiUncaughtHandler(  231):     at ti.modules.titanium.ui.TableViewProxy.handleMessage(TableViewProxy.java:466)
E/TiUncaughtHandler(  231):     at android.os.Handler.dispatchMessage(Handler.java:95)
E/TiUncaughtHandler(  231):     at android.os.Looper.loop(Looper.java:123)
E/TiUncaughtHandler(  231):     at android.app.ActivityThread.main(ActivityThread.java:4203)
E/TiUncaughtHandler(  231):     at java.lang.reflect.Method.invokeNative(Native Method)
E/TiUncaughtHandler(  231):     at java.lang.reflect.Method.invoke(Method.java:521)

You can cause an FC using this app.js + win.js + table.js:

app.js:

Titanium.UI.setBackgroundColor('#000');
Titanium.UI.createWindow({  
    title:'Test',
    backgroundColor:'#fff',
    fullscreen: true,
    exitOnClose: true,
    url: 'win.js'
}).open();

win.js:

var win = Ti.UI.currentWindow;
var btn = Ti.UI.createButton({
    title: 'Open 2nd Window'
});
btn.addEventListener('click', function(){
    Ti.UI.createWindow( {
        fullscreen:true,
        url: 'table.js',
        backgroundColor: 'black'
    }).open();
});
win.add(btn);

table.js:

var win = Ti.UI.currentWindow;
var tv = Ti.UI.createTableView();
tv.setData( [ Ti.UI.createTableViewRow({ title: 'Loading...' }) ] );
win.add(tv);

// Now start a second thread that will update the table
setTimeout(function() {
    for (var i = 1; i <= 1000; i++) {
        tv.insertRowBefore(0, 
            Ti.UI.createTableViewRow( {title: 'New row ' + i} ));
    }
}, 50);

When you run it and you open the second window, click your hardware back button while the table is being assembled. After you get back to the first window, just wait a while and it'll crash.