boost.m4: when given --with-boost, don't pick up system libs first.
boost.m4: when given --with-boost, don't pick up system libs first.

	Serial 11.
	* build-aux/boost.m4 (BOOST_REQUIRE): Don't even try -IDIR if
	DIR/boost/version.hpp does not exist.

aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport