Support for old NeXTstep 3.3 sed. * m4/absolute-header.m4 (gl_ABSOLUTE_HEADER_ONE): In the sed address part, use /.../, not \|...|. Escape periods in the header file name. * m4/include_next.m4 (gl_NEXT_HEADERS_INTERNAL): Likewise. Reported by Daniel Richard G. <skunk@iskunk.org>.