check for python >= 2.7

a29fca70 requires subprocess.check_output
which was added with Python 2.7

configure.ac

@@ -345,11 +345,20 @@ else
 fi
 
 AM_MISSING_HAS_RUN
-AC_CHECK_PROGS(PYTHON, [python3 python3.1 python3.2 python2.7 python2.6 python2.5 python2 python], "no")
+AC_CHECK_PROGS(PYTHON, [python3 python3.1 python3.2 python2.7 python2 python], "no")
 if test "x$PYTHON" = "xno"; then
-  AC_MSG_ERROR([Python is needed to build Varnish, please install python.])
+  AC_MSG_ERROR([Python is needed to build Varnish, please install python 2.7 or later.])
 fi
 
+py_ver=`"$PYTHON" -V 2>&1`
+case "$py_ver" in
+Python?3.* | Python?2.[7-9].*)
+	;;
+*)
+	AC_MSG_ERROR([Python >= 2.7 is required])
+	;;
+esac
+
 AC_CHECK_DECL([SO_ACCEPTFILTER],
     AC_DEFINE(HAVE_ACCEPT_FILTERS,1,[Define to 1 if you have accept filters]),
     ,