Update .gitignore (partly per Antoine, partly from experiments locally).
Make prerendered buttons work on Android.

This change switches from using BitmapUtil.scaledDrawableFromStream to
load prerendered buttons to using Drawable.createFromStream.  Needs
testing with more devices, and seems to have trouble with
_non_-prerendered stuff at the moment...
Include build.xml, ditch module.a and module.jar.
Bump to 2.5.3.
Fix image scaling for prerendered: true on Android.
Support prerendered: true for addButton on Android.