[4.0] 71b6a5d Correct AC_CHECK_PROGS usage

[Lasse Karstensen]

commit 71b6a5da74278a7814459a48a2ebbd6dbf60f5d5
Author: Federico G. Schwindt <fgsch at lodoss.net>
Date:   Tue Jul 8 10:59:20 2014 +0100

    Correct AC_CHECK_PROGS usage

diff --git a/configure.ac b/configure.ac
index 118f743..ced8495 100644
--- a/configure.ac
+++ b/configure.ac
@@ -321,7 +321,10 @@ else
 fi
 
 AM_MISSING_HAS_RUN
-AC_CHECK_PROGS(PYTHON, [python3 python3.1 python3.2 python2.7 python2.6 python2.5 python2 python], [AC_MSG_ERROR([Python is needed to build Varnish, please install python.])])
+AC_CHECK_PROGS(PYTHON, [python3 python3.1 python3.2 python2.7 python2.6 python2.5 python2 python], "no")
+if test "x$PYTHON" = "xno"; then
+  AC_MSG_ERROR([Python is needed to build Varnish, please install python.])
+fi
 
 AC_CHECK_DECL([SO_ACCEPTFILTER],
     AC_DEFINE(HAVE_ACCEPT_FILTERS,1,[Define to 1 if you have accept filters]),