maint: don't leak developer GREP, SED etc into distribution file.

maint: don't leak developer GREP, SED etc into distribution file.

* Makefile.am: Having rearranged the file, now apply the actual
changes to follow-up.
(edit): Split into two parts...
(bootstrap_edit): ...substitutions that should happen at bootstrap
time...
(configure_edit): ...and substitutions that should not happen until
configure time.
* Makefile.am (libltdl/m4/ltversion.m4, libltdl/config/ltmain.sh)
(libtoolize.in, tests/package.m4): Use bootstrap_edit.
(libtoolize, tests/defs): Use configure_edit.
* HACKING (Release Procedure): Remove the note to workaround the
bug fixed by this changeset.
* NEWS (Bug fixes): Mention that this bug is now fixed.
Reported by Joerg Sonnenberger.