Log Message:
xlock -mode dclock would segfault on OSes with sizeof(time_t)>sizeof(long);
this includes NetBSD-6 on 32bit systems.

As a result, xlock -mode random (the default) would eventually unlock
the screen, without the user being aware of this (as she/he's can be
presumed to have left the monitor).

The reason was that some variables in dclock.c were declared long, but
contain essentially time_t values. In on case, a pointer to such a
variable was casted to (struct time_t *) and passed to localtime(),
and the resulting pointer is not checked for error before being used.

The variables have been changed to time_t and the typecast has been
removed.