Restore its ability to reject a string longer than will fit within
size_t that was lost by moving away from strnlen(). Determine the
length inline rather than using strlen().
Move it from hacklib.c to alloc.c so that utility programs have easy
access, and remove the copy of it from dlb_main.c.
Fix a logic bug in str_start_is(). If a string was considered to
be too long, it exited the loop when n was 0 but also performed
post-decrement. So after the loop, n would be -1 and the 'if (n==0)'
test would fail. panic() would occur if the initial string matched
and happened to be LARGEST_INT-1 characters long.
1c08982d56