Support android 4.4.

This is our initial attempt at supporting Android 4.4.  There are a few major caveats:

* Because Android 4.4 adds support for Java 7, we had to convert Robolectric to use Java 7.  This is because AOSP references classes that are only included in the Java 7 JDK (`AutoCloseable` in particular).  This also means that apps using Robolectric will need to be compiled against Java 7.

* Because the bytecode format of Java 7 has changed, tests need to be run with the `-XX:-UseSplitVerifier` flag so the ClassLoader will not complain about missing stack maps.  This could probably be fixed by changing the `AsmInstrumentingClassLoader`, but we lacked the knowledge to make this change.  @xian, we could use your help here.

We'd like people to test out this branch against other apps, since there are probably changes that we missed.  Also, because this will break backwards compatibility, it might make sense for this change to be part of a 3.0 release.

We've uploaded the android-all-4.4_r1 artifacts to Sonatype.  We'll hold off on releasing them until this issue is closed.