autogen.sh: fail after tools check

The script should fail _after_ checking that the needed tools are
installed.

The problem was that if autoconf is NOT installed then the script just
exit with no error message. No we have:
Please install autoconf and rerun this script !

autogen.sh

@@ -5,9 +5,6 @@
 #
 # Requires: automake, autoconf, dpkg-dev
 
-# fail on error
-set -e
-
 #
 # Check if autoconf and automake are installed
 #
@@ -32,6 +29,9 @@ then
 	echo "Error: directory $PATH_AUTOMAKE does not exist"
 fi
 
+# fail on error
+set -e
+
 # Refresh GNU autotools toolchain.
 for i in config.guess config.sub missing install-sh mkinstalldirs ; do
 	test -r $PATH_AUTOMAKE/${i} && {