With --enable-memchecker builds, use calloc(3) for OBJ_NEW instead of
malloc(3). This cuts down on a lot of valgrind/memory checker false
positive output.
Also make a minor change in the valgrind configure.m4; have it assign
0xf to a char. The prior assignment (of 0xff) was warning about an
overflow. This didn't really matter, but we might as well make the
test not have a gratuitious warning in it.
a422d893b8