bisect: use "git rev-parse --sq-quote" instead of a custom "sq" function

bisect: use "git rev-parse --sq-quote" instead of a custom "sq" function

As the "sq" function was the only place using Perl in "git-bisect.sh",
this removes the Perl dependency in this script.

While at it, we also remove the sed instruction in the Makefile that
substituted @@PERL@@ with the Perl path in shell scripts, as this is
not needed anymore. (It is now only needed in "git-instaweb.sh" but
this command is dealt with separately in the Makefile.)

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>