Call string_list_split() for cutting a space separated list into pieces
instead of reimplementing it based on struct strategy. The attr member
of struct strategy was not used split_merge_strategies(); it was a pure
string operation. Also be nice and clean up once we're done splitting;
the old code didn't bother freeing any of the allocated memory.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>