increase number of walker to 4

./scripts/assembly_debugging/SAMN02402663-Mtuberculosis-spate-4x8.sh

Before (1 actor / worker):
3m4.194s

After (4 actors / worker):
3m4.283s

Link: https://github.com/GeneAssembly/biosal/issues/660
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
add progress information for unitig building

./scripts/assembly_debugging/SAMN02402663-Mtuberculosis-spate-4x8.sh

2m50.884s

[boisvert@bigmem biosal]$ ./scripts/assembly_debugging/check-names.sh 1.fasta
Got names
Got defect names
Check DefectList.txt (defects: 0 / 1796)
4 longest:
44509
44509
44509
44509

Link: https://github.com/GeneAssembly/biosal/issues/658
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
skip a start vertex when it is grabbed by someone else

Link: https://github.com/GeneAssembly/biosal/issues/651
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>