Stop using "Int" for microsecond delays in "base"

[Liyang HU]

Paul Johnson <paul <at> cogito.org.uk> writes:
> The "base" library has the "threadDelay" primitive, which takes an Int 
> argument in microseconds.

I always end up with a wrapper around it, taking a NominalDiffTime; I could
never be sure whether threadDelay interpreted its argument as
milli-/micro-/nano-seconds without looking it up.

For lack of Data.Time in base, how about Data.Fixed.Pico?

Cheers,
/Liyang