Kawa support for JDK 1.7

[Per Bothner]

I checked in various fixes to enable Kawa running under JDK 1.7
using working StackMapTable attributes, which replaces use of the
traditional bytecode verifier.  Kawa has generated StackMapTable
for a while, but there were some bugs which didn't show up except
when setting the class-file Major Version to 51 (i.e. for Java 7).

This code was difficult to get working, so it would be good to get
more testing.  If you have an application written in Kawa that you'd
like to try with JDK 1.7, get Kawa from SVN, and pass the option
   --with-java-source=6
to the configure command line.

If using Ant do:
   ant select-java7 all

We don't really make use of JDK 1.7 features yet.  There is a
throw-away use of MethodHandles, but that is only used at
compile-time to find opimization methods.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/