cal: don't mix ncurses output functions and printf()

Fedora 18 (ncurses-libs-5.9-7.20121017, glibc-2.16-28):

$ cal | cat
Actual results:
    January 2013    Su Mo Tu We Th Fr Sa       1  2  3  4  5 6  7  8
9 10 11 1213 14 15 16 17 18 1920 21 22 23 24 25 2627 28 29 30 31

Not sure where is the problem, but it's too fragile to mix two
output methods in one code.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=896447
Signed-off-by: Karel Zak <kzak@redhat.com>