cal: fix weekday alignment for certain locales

cal: fix weekday alignment for certain locales

For example this had too much padding: LANG=zh_CN.utf8 cal -j
while this had too little padding:     LANG=hu_HU.utf8 cal
This had invalid chars:                LANG=li_BE.utf8 cal
This had too few chars:                LANG=si_LK.utf8 cal

Note some locales may display with slightly worse alignment
(fa_IR.utf8 for example), but that is only because the terminal
is not merging the combining characters. This happens on
gnome-terminal-2.18.3-1.fc8 at least.

Signed-off-by: Pádraig Brady <P@draigBrady.com>
Signed-off-by: Karel Zak <kzak@redhat.com>