Initial implementation of instrumenting proxy server.

Note that the proxy will not work without a separate library
that is not yet available in open source.

Includes some related refactoring of esnstrument.js.
rename functions that operate on IID map file
quick hack to add an option to keep trace in memory
Add ability to stop tracing in browser.

One can stop tracing by pressing Alt-Shift-T.  For now, the user
gets an alert when the shortcut is pressed, and when all remaining
trace elements have been flushed.
was checking wrong flag before
minor cleanup
change to catch keydown instead of keypress
Optimize trace flushing.

Rather than flushing at every function exit, we only
flush when the call stack is almost empty.