The location of the nagios plugin source has changed.

Now on github, in another repo than the varnish sources.
2.1: the commit 70e4ded1221846d4149dd743e2ac634946c313ad has the svn tag 4009
2.0: the commit a64abfb7e70fd1f6b53ff64f9ddeafb7209c0b23 is the last one were the MAC_STAT macro has 4 arguments.

Sources for varnish are now here:
https://github.com/varnish/Varnish-Cache

and nagios plugin:
https://github.com/varnish/varnish-nagios

I tried to be as close as possible from the old svn (vanished) configuration.