Part of #447.
* configure.ac, m4/debug.m4, m4/devel.m4, m4/gccoptim.m4,
m4/ndebug.m4: Replace AC_ERROR and AC_HELP_STRING by
by AC_MSG_ERROR and AS_HELP_STRING.
Part of #184.
* m4/devel.m4 (adl_ENABLE_GLIBCXX_DEBUG): New macro.
* configure.ac: Use it.
* README: Mention it.
* spot/twa/acc.cc: Fix a small issue found with this
option.
* configure.ac: Do not add CXXFLAGS and CFLAGS in ac_configure_args,
it causes problem when using config.cache. Instead ...
* m4/devel.m4: Add --enable-devel or --disable-devel on
ac_configure_args, now that BuDDy understands that.