number of threads needs to be specified by user, otherwise software crashes

[rchikhi]

When running Tandemmapper on its test data:

./tandemmapper.py --nano test_data/simulated_reads.fasta -o tandemRes test_data/simulated_del.fasta

Error is:

  File "TandemTools/scripts/make_alignments.py", line 201, in <listcomp>
    for assembly in assemblies if not exists(assembly.bed_fname) or no_reuse],
TypeError: unsupported operand type(s) for //: 'NoneType' and 'int'

A simple fix is for the user to add -t 1 to the command line, and then it doesn't crash.