some hg38 builds have e.g. phix where others do not.
this means that bin files can differ by that single tid.
here, we try this:
user specifies fasta file indicating minimal genome (without phix).
if this is not sent in to merge (via --fasta), then the first bin
file indicates the expected genome content.
if a bin file is specified that contains a chromosome not found in
the minimal genome (e.g. it has phix), then any tread with that chrom
is mapped to tid=-1 (unmapped).
in addition, all tids are remapped to the expected, given target
genome ordering
To Do
some hg38 builds have e.g. phix where others do not. this means that bin files can differ by that single tid. here, we try this:
this all takes place in unpack_file