In addition to updating the xstrdup(mkpath(...)) call sites with
mkpathdup(), we also fix a memory leak (in merge_3way()) caused by
neglecting to free the memory allocated to the 'base_name' variable.
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>