JDK6 runtime support for json

Warning: the backported try-with-resources are not pretty
I was wondering this also.  It looks like string switch doesn't become faster until somewhere around the 16th test (string switch is slower here because the strings are fresh from json parsing and don't already have hashCode calculated).  See https://github.com/trask/baseline-microbenchmarks/blob/master/src/main/java/com/github/trask/microbenchmarks/StringSwitchBenchmark.java.