by default current prefix is also searched
allow to specify libb2 location, by using --with-bz2-prefix,
by default current prefix is also searched
locating gmp and bz2 works by default on OpenBSD (bb #301)
move local m4 macros to m4/
import lib-link.m4 and dependent files
quoting for autoconf macros (bb #452)
git-svn: trunk@3566
