Ensure we close the packfile after creating it in fast-import.

Because we are renaming the packfile into its file destination we
need to be sure its not open when the rename is called, otherwise
some operating systems (e.g. Windows) may prevent the rename from
occurring.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -645,6 +645,7 @@ static void fixup_header_footer()
 
 	SHA1_Final(pack_data->sha1, &c);
 	write_or_die(pack_fd, pack_data->sha1, sizeof(pack_data->sha1));
+	close(pack_fd);
 }
 
 static int oecmp (const void *a_, const void *b_)
@@ -768,14 +769,11 @@ static void end_packfile()
 		if (!new_p)
 			die("core git rejected index %s", idx_name);
 		new_p->windows = old_p->windows;
-		new_p->pack_fd = old_p->pack_fd;
 		all_packs[pack_id++] = new_p;
 		install_packed_git(new_p);
 	}
-	else {
-		close(pack_fd);
+	else
 		unlink(old_p->pack_name);
-	}
 	free(old_p);
 
 	/* We can't carry a delta across packfiles. */