Disable DalvikVM GC logcat spam

Dalvik logs everytime a garbage collection is run. Disabled to remove
clutter from logcat. Can be renabled by #defining DEBUG.

Change-Id: I57a461857f8d0ecbf223f3c18187f62095adb5b4
Some changes added to compile and run with Java 6 and Java 7.

* correction of errors with Javac 6:
- target 1.5 and source empty.