Small optimizations 1

A couple of small optimizations.
This is essentially what the EXECUTION_TIME constant does.

But you're right.
I checked how many operations were processed within the EXECUTION_TIME across several PDFs and saw that the very minimum number was around 4-500 on my machine, and up to 30.000+. That's a lot of calls to `Date.now()` for nothing ... except I overlooked that my setup is pretty decent and this number of operations could well go as low as 40-50 on another machine.

How do you feel about using `var EXECUTION_STEPS = 10;` ?

I will run some tests to see the "cost" of the operations when batched by 10 to see whether the possibility of a "long running script" dialog is serious or that small batches contain at most one expensive operation and all the other ones are cheap.