This changes breakpoint_ops::print_one to return bool, and updates all
the implementations and the caller. The caller is changed so that a
NULL check is no longer needed -- something that will be impossible
with a real method.
The "catch load" code is reasonably self-contained, and so this patch
moves it out of breakpoint.c and into a new file, break-catch-load.c.
One function from breakpoint.c, print_solib_event, now has to be
exposed, but this seems pretty reasonable.
