Implement shellcheck advice

[kresp0]

Yellow warnings:

In txt2gb.sh line 225:
    tr [:lower:] [:upper:] < $TMPDIR/txt > $TMPDIR/TXT
       ^-------^ SC2060: Quote parameters to tr to prevent glob expansion.
                 ^-------^ SC2060: Quote parameters to tr to prevent glob expansion.

In txt2gb.sh line 432:
    for LONGCOUNTER in {1..6}; do
    ^-^ SC2034: LONGCOUNTER appears unused. Verify use (or export if used externally).

Green warning: many