revision: replace "struct cmdline_pathspec" with argv_array

revision: replace "struct cmdline_pathspec" with argv_array

We assemble an array of strings in a custom struct,
NULL-terminate the result, and then pass it to
parse_pathspec().

But then we never free the array or the individual strings
(nor can we do the latter, as they are heap-allocated when
they come from stdin but not when they come from the
passed-in argv).

Let's swap this out for an argv_array. It does the same
thing with fewer lines of code, and it's safe to call
argv_array_clear() at the end to avoid a memory leak.

Reported-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>