Per the emscripten devs, it's not necessary (any more?).  This (condensed) chat on IRC made me remove it:

> me: I'll see "initializing" on the canvas and they'll get as far as the abort, and then nothing
> azakai: what abort?
> me: the abort I thought was normal
> me: if you watch the error console, you'll see an uncaught abort and then nothing
> DFJustin: jsmess used an abort as a cheap hack to switch to async execution without rewriting the codebase
> azakai: i see there is an anort right after the set main loop
> azakai: just call set main loop with last parameter set to 1
> azakai: and remove the abort
> DFJustin: azakai: this was originally written before emscripten_set_main_loop() existed and then converted to use it, might just have missed an opportunity to simplify it at that time
> azakai: got it