strvec: rename files from argv-array to strvec

This requires updating #include lines across the code-base, but that's
all fairly mechanical, and was done with:

  git ls-files '*.c' '*.h' |
  xargs perl -i -pe 's/argv-array.h/strvec.h/'

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -20,7 +20,7 @@
 #include "hashmap.h"
 #include "ll-merge.h"
 #include "string-list.h"
-#include "argv-array.h"
+#include "strvec.h"
 #include "graph.h"
 #include "packfile.h"
 #include "parse-options.h"