ul: use size_t to measure memory allocation size

ul: use size_t to measure memory allocation size

The size_t is the type libc memory allocation functions use.  The size_t
also provides allocation range that is enough not to a simple tool like this
to perform paranoia size checks.  Just let the realloc(3) fail if there is
not enough memory available to handle the requested line size.  That is a
lot more straightforward.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>