maint: use $SED and $GREP, not sed and grep in all scripts.
Choosing between hardcoding a tool's name, or using the shell
variable with a path to the user's prefered implementation or
configure's idea of the best available is a premature
optimisation.
* build-aux/ltmain.in, gl/build-aux/bootstrap.in,
gl/build-aux/extract-trace, gl/build-aux/funclib.sh,
libtoolize.in: Use $SED and $GREP consistently throughout,
instead of hardcoding sed and grep.
* bootstrap: Regenerate.
Signed-off-by: Gary V. Vaughan <gary@gnu.org>