scripts/global: remove redundant `in "$@"` in inarray.
scripts/globals: add slice (split array by delimiter).
Add scripts/fd: streams and fd operations.
scripts/globals: enable extglob for framework.

It's useful.
scripts/setconf: support streams in getconf.

Use output duplication function to peep into sed's output
and check if it's not empty (and build retval accordingly).

This also gets rid of grep.
scripts/setconf: support streams in setconf.

This is tougher than getconf. Now there are two variants of setconf:
regular file-based (grep + in-place sed, as it was) and streamed.

Streamed variant works also by stdout duplication, but in this case
input is duplicated (using cat as stdout generator) and processed using
grep and sed in stream mode. Note that here we still need to use grep.
scripts/fd: document exit code of clone_output_to_command.