Creating .dotest-merge before validating the options prevents both
--continue and --interactive from working if the options are invalid,
so only create it after validating the options.
[jc: however, just moving the creation of DOTEST breaks output]
Signed-off-by: Matt Kraai <kraai@ftbfs.org> Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>