pathspec: add copy_pathspec

Because free_pathspec wants to free "items" pointer in the pathspec
structure, a simple structure assignment is not enough if you want to
copy an existing pathspec into another.  Freeing the original will
damage the copy unless a deep copy is made.

Note that the strings in pathspec->items->match and the array
pathspec->raw[] are still shared between the original and the copy.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pathspec.c

@@ -249,3 +249,11 @@ const char **get_pathspec(const char *prefix, const char **pathspec)
 		return NULL;
 	return pathspec;
 }
+
+void copy_pathspec(struct pathspec *dst, const struct pathspec *src)
+{
+	*dst = *src;
+	dst->items = xmalloc(sizeof(struct pathspec_item) * dst->nr);
+	memcpy(dst->items, src->items,
+	       sizeof(struct pathspec_item) * dst->nr);
+}