Backend JS engine upgrade

[Adam Bliss]

In anticipation of my codeWriter proposal passing, I have upgraded the
server's javascript engine from JavaScript-1.03/SpiderMonkey 1.60 to
JavaScript-1.04/SpiderMonkey 1.70. the exception handling in the
former was not quite correct, and it made my subgame nonfunctional. I
believe it will work now. There was a bit of downtime in the process,
which I hope nobody ran into.

I also made a backend change that limits the total number of branches
to 1 million. This is to prevent some wisecracker from writing
while(true){} and locking up the webserver. I think this number
should be high enough for all practical purposes (it can do an entire
500-step round of CodeWriter), but if you find that it is not, let me
know.

In the spirit of open testing, I have also created a
server-side-sandbox at http://ecmanomic.org/test.html . This has a
backend identical to the real thing, except that it runs in sandbox
mode (so that the "debug" function works). Feel free to use this to
test out server-side JS bugs (and report your findings on the group
page devoted to that topic). Don't abuse it too much (e.g. trying to
crash the webserver) or I'll have to remove it.

Cheers,
--abliss