hexdump: use xcalloc()

Reported-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Karel Zak <kzak@redhat.com>
hexdump: don't access hex after freeing it

[kzak@redhat.com: - remove unnecessary code]

Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Karel Zak <kzak@redhat.com>
hexdump: convert a variable type according with fmt

hexdump works uncorrectly on Rassberry Pi (raspbian wheezy):
0000000 3200000000 3400000000 3600000000 3800000000 a00000000
000000a

The problem is that the %qx format is used for printing
the (short int) variable.

Here is the output from hexdump with this patch:
0000000 3231 3433 3635 3837 0a39
000000a

Currently raspbian uses hexdump from bsdmainutils.
bsdmainutils: /usr/bin/hexdump

Signed-off-by: Andrew Vagin <avagin@openvz.org>