Merge branch 'mh/import-transport-fd-fix' into maint

The ownership rule for the file descriptor to fast-import remote
backend was mixed up, leading to unrelated file descriptor getting
closed, which has been fixed.

* mh/import-transport-fd-fix:
  Use xmmap_gently instead of xmmap in use_pack
  dup() the input fd for fast-import used for remote helpers

packfile.c

@@ -640,7 +640,7 @@ unsigned char *use_pack(struct packed_git *p,
 			while (packed_git_limit < pack_mapped
 				&& unuse_one_window(p))
 				; /* nothing */
-			win->base = xmmap(NULL, win->len,
+			win->base = xmmap_gently(NULL, win->len,
 				PROT_READ, MAP_PRIVATE,
 				p->pack_fd, win->offset);
 			if (win->base == MAP_FAILED)