First cut ast AST utilities module, plus a couple tests.

This mostly has code copied from esnstrument.js, plus
a routine to deserialize ASTs.  Eventually, we should
get rid of the code in esnstrument.js and have it refer
to this module.
make esnstrument.js depend on astUtil.js

still need to fix and test browser and proxy server
fix browser tests and proxy server to add astUtil.js
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