remove ARPACK files from sources and restore configure checks for external ARPACK library * libcruft/arpack: Remove directory and all files. * libcruft/Makefile.am: Don't include arpack/module.mk. * m4/acinclude.m4 (OCTAVE_CHECK_ARPACK_OK): New macro. * configure.ac: Check for ARPACK. Use OCTAVE_CHECK_ARPACK_OK to test for known bug. * build-aux/common.mk (ARPACK_CPPFLAGS, ARPACK_LDFLAGS, ARPACK_LIBS): Restore variables. (do_subst_config_vals): Substitute them. * eigs-base.cc: Use HAVE_ARPACK again. * sparse/svds.m: Use "testif HAVE_ARPACK" instead of "test". * DLD-FUNCTIONS/eigs.cc (Feigs): Restore HAVE_ARPACK conditionals. Use "testif HAVE_ARPACK" instead of "test". * toplev.cc (octave_config_info): Restore ARPACK_CPPFLAGS, ARPACK_LDFLAGS, ARPACK_LIBS to the struct. * oct-conf.h.in (OCTAVE_CONF_ARPACK_CPPFLAGS, OCTAVE_CONF_ARPACK_LDFLAGS, OCTAVE_CONF_ARPACK_LIBS): Restore #defines.