bibisect on linux and libboost system libs -> orcus

So,

with internal boost (iow not system-boost) build, we seems
to build/deliver only static boost lib not the *.so
but liborcus, although it is configured to use the internal boost,
still will pick up the system .so (somewhere else than told) for boost
and not use these static libs

in turn that means that when using bibisect on a linux box that does
not have these boost library installed (or too old I guess), we got
missing library failure.

I peeked at configure.ac in liborcus, and I was suspecting that adding
BOOST_STATIC may do the trick... but we use configure directly in
external/liborcus.. so patching autogen.ac directly there is prolly
not the way to go...
Note: I'm not sure that BOOST_STATIC is an answer, even less the
'right(tm)' answer

Norbert