Meryl-lookup runs single threaded in phase_block regardless of thread count about merqury

[ASLeonard]

Great, thanks Brian.

I commented out that line from AS_configure, and the threading now responds to the OMP variable without the need for the explicit -threads param. Merqury back to being super quick!

[brianwalenz]

For such a simple bug, the phenotype is surprisingly complicated.

It's only affecting OMP_NUM_THREADS. Using any other environment variable (e.g., SLURM_JOB_CPUS_PER_NODE) to set the number of threads to use works as expected.

Meryl isn't affected because it queries the number of threads allowed before AS_configure() is called, while meryl-lookup calls AS_configure() first.

I think the correct fix is to remove omp_set_num_threads(1) from AS_configure(). This was added to disable OpenMP parallelization of std::sort, but we're now doing that through a different mechanism. For meryl/merqury removing this should be safe; it was canu that had problems here.