Add support for dependencies between boost libraries in BOOST_FIND_LIB.
Add support for dependencies between boost libraries in BOOST_FIND_LIB.

Just for the fun I measured that this macro can make up to 80 link
attempts before failing...

	* build-aux/boost.m4: (BOOST_FIND_LIB): Accept and pass an extra
	  boost lib as dependency.
	  (BOOST_FILESYTEM): Pass system as dependency to BOOST_FIND_LIB.

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