Require Python >= 3.4 at build time

Until the naked "python" executable refers to python3 (currently it is
still python2) it now takes lower precedence.

varnish-legacy.m4

@@ -98,9 +98,10 @@ AC_SUBST([VMOD_DIR])
 
 AC_DEFUN([VARNISH_VMODTOOL],
 [
-AC_CHECK_PROGS(PYTHON, [python3 python3.1 python3.2 python2.7 python2.6 python2.5 python2 python], "no")
+AC_CHECK_PROGS(PYTHON, [python3.9 python3.8 python3.7 python3.6 python3.5 dnl
+  python3.4 python3 python, "no"])
 if test "x$PYTHON" = "xno"; then
-  AC_MSG_ERROR([Python is needed to build, please install python.])
+  AC_MSG_ERROR([Python >= 3.4 is needed to build, please install python.])
 fi
 VARNISH_PKG_GET_VAR([VMODTOOL], [vmodtool])
 AC_SUBST([VMODTOOL])

varnish.m4

@@ -130,10 +130,10 @@ AC_DEFUN([_VARNISH_CHECK_DEVEL], [
 # ---------------------
 AC_DEFUN([_VARNISH_CHECK_PYTHON], [
 	m4_define_default([_AM_PYTHON_INTERPRETER_LIST],
-[python3.9 python3.8 python3.7 python3.6 python3.5 python3.4 python2.7 dnl
-python python2 python3])
-	AM_PATH_PYTHON([2.7], [], [
-		AC_MSG_ERROR([Python >= 2.7 is required.])
+		[python3.9 python3.8 python3.7 python3.6 python3.5 dnl
+		python3.4 python3 python])
+	AM_PATH_PYTHON([3.4], [], [
+		AC_MSG_ERROR([Python >= 3.4 is required.])
 	])
 
 ])