only run precompile workload when generating output

[sjkelly]

otherwise we run code at module load each time.

[KristofferC]

otherwise we run code at module load each time.

This is not really true, the toplevel code only runs during precompilation (or if you load the module and have turned off precompilation).

[StefanKarpinski]

Seems like this change is desirable so that this code isn't run when recompilation is off though, no?

[sjkelly]

I should have clarified that the main rationale for this is to make Downloads work at using time with juliac. I am not sure if juliac's compilation model is broken, but I felt that regardless this would be a strict improvement.

I supposed backwards compat needs to be fixed as well.

[sjkelly]

Note that #242 is also required for juliac compatibility.

[KristofferC]

This fails on earlier julia versions, I think you need to use the ccall to be compatible.