clean up open() functions to use self.auto() which does compression for us based on the file extension

update _const_dt to include a wrapper just before it's cached, allowing output to the screen for debugging

other minor fixes

add automatic cacheing of various functions, and a cache_test() routine to test the runtimes with and without caching

the joiningfile is now made by whichever job gets to this task first, so the error where it wasn't fully made (when jobs were slowly run from the HPC queue) should not happen now unless it takes a long time to write that one short file. I guess we could put in a checkfile if required, but this should be *very* rare.

all other files access the HPC API, not the slurm and condor objects directly