Boost is now required (ticket:370). Boost 1.33 is required, which is a
pretty arbitrary number. I happen to have 1.33 installed on my
machine. If someone can test that it works with an earlier version, I
am more than happy to soften this requirement. Currently, there is no
linking to Boost. I added a file yat.am that is included in most of
our Makefile.am, to avoid parallel modifications.