Since 2f644c8c (barvinok_bound: use isl to split on domain size,
Sat Aug 28 10:51:23 2010 +0200), only the functions declared
in <barvinok/isl.h> are used.  Now that this header is included
directly, the include of <barvinok/barvinok.h> can be removed.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>