cal: limit year to 32 bit value

cal: limit year to 32 bit value

This is done to keep things simple, when considering tests, for both 64
and 32 bit architectures.  Setting the upper limit of a year value to to
2^31-1 (2147483646) should be enough for anyone.

Reported-by: Mike Frysinger <vapier@gentoo.org>
Reference: http://www.spinics.net/lists/util-linux-ng/msg08662.html
Signed-off-by: Sami Kerola <kerolasa@iki.fi>