Incorrect 'usable bases' column in stats file

The maximum size of an integer in the busybox implementation of wc (which is used in the biocontainers we use with singularity) is 2^32, which is only 4 billion. When counting the number of bases in a bam file for the stats.tsv file, we go over this limit, causing the counter to reset to 0. As a result, the number of usable bases that is reported in the stats.tsv file is much lower than the actual count.

This problem was introduced when we switched to singularity.