TOOLS/idet.sh: remove unused and duplicated assignments
TOOLS/idet.sh: add description

Just a copy of c0cd58e3f5b1daff58ad5ca48b964a2b1fb86d6d commit message
(with a small fix: ildetect.sh+ildetect.so, not
ildetect.sh+ildetect.sh).
TOOLS/mpv_identify.sh: remove pointless escape
TOOLS/umpv: use python octal notation