The `last-postmask` tool distributed with [LAST](https://gitlab.com/mcfrith/last)
filters alignments in a MAF file to remove those with too many masked
(lower-case) positions compared with their score.
As other filter modules like `last/split`, its output file risks to
overwrite its input file as their names are constructed from the sample
ID when multiple filters are chained in the pipeline. I added a check
that gives a clearer error message in this case. Please let me know
what you think about; I can add this test to the existing LAST modules
as well.
This new module is part of the work discribed in Issue #464. During this
development, we fix the version of LAST to 1219 to ensure consistency.
We will upgrade it later.
