Add BuildConfig to ant SDK project.

The BuildConfig class contains a single boolean constant
called DEBUG which is true only for debug/instrumented builds.

This allows developers to create debug only code that's automatically
stripped from release builds.

Also fixed some issues with dependency check for other tasks, notably
the aapt task that would always find new files due to not filtering
out files that are ignored by aapt itself (hidden files, version control
files, etc...)

Change-Id: I4391a87c064a185d6b337ca46e3a9f0e43c5174d
11 files changed