Add missing header file to tarball

Fixes build failure


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3549 d4fa192b-c00b-0410-8231-f00ffab90ce4

include/Makefile.am

@@ -26,6 +26,7 @@ nobase_noinst_HEADERS = \
 	libvarnish.h \
 	libvcl.h \
 	miniobj.h \
+	purge_vars.h \
 	vsha256.h \
 	vqueue.h \
 	vpf.h \