multiproc is star_hsml unaware for same snapshot

[agurvich]

multiprocessing on multiple perspectives will compute smoothing lengths for each perspective even though you only have to compute them once... should put a flag or something to check if this is going to happen before mapping to the pool.

[agurvich]

this is a comment for interpolator and star_movie_maker though star_movie_maker can't loop through multiple perspectives from the command line anyway right now...

[agurvich]

This shouldn't happen now that getHSML is @metadata_cache'd. I'll need to make sure that only one thread actually computes it for the first time though, then they should all be able to read the smoothing lengths. Leaving open as a reminder.