[TIMOB-17674] Android: On Android Ti.UI.ImageView can show the wrong image (cache bug, explained)

If an application has two different images with urls/paths that map to the same hash code at java.lang.String level then Ti.UI.ImageView can show the wrong one. TiUIImageView internally uses a memory cache for the Bitmaps with TiDrawableReference.hashCode() as keys. In case of an url-based drawable reference TiDrawableReference.hashCode() turns into a simple java.lang.String.hashCode(url) wrapper. See line 115 of https://github.com/appcelerator/titanium_mobile/blob/master/android/titanium/src/java/org/appcelerator/titanium/view/TiDrawableReference.java and line 694 of https://github.com/appcelerator/titanium_mobile/blob/master/android/modules/ui/src/java/ti/modules/titanium/ui/widget/TiUIImageView.java java.lang.String.hashCode() is very likely to generate collisions. The following code prints the same number for both urls.

	public static void main(String[] args)
	{
		int h1 = "file:///data/data/it.xenesys.Nomination/app_appdata/ITEMFASHION_0002TW1.png".hashCode();
		int h2 = "file:///data/data/it.xenesys.Nomination/app_appdata/ITEMFASHION_0002TVP.png".hashCode();
		System.out.println("Hash code 1: " + Integer.toString(h1));
		System.out.println("Hash code 2: " + Integer.toString(h2));
	}

The cache should use a stronger hashing algorithm (such as SHA1) and possibly add more data to be hashed (the file size?).