openvpn: improved to build plugins (see note)

Note:

This commit is improving the openvpn package to build the included
plugins if possible (currently only the pam authentication plugin
if pam is installed), but also introducing the 'plugins_enabled'
variable within the openvpn.conf file which can be used to define
a space seperated list of plugins which should be build additionally.

This will offer a convinient way for targets which patch in custom
plugins to enable them within the build process of the package.
The only thing to do is to append the desired plugin to then list
stored within the $plugins_enabled variable.

Example: Adding 'myplugin' within a target specific 'openvpn.conf'
--------------------------------------------------------------------
var_append plugins_enabled ' ' "myplugin"
--------------------------------------------------------------------

network/openvpn/openvpn.conf

@@ -2,7 +2,7 @@
 # This copyright note is auto-generated by ./scripts/Create-CopyPatch.
 #
 # Filename: package/.../openvpn/openvpn.conf
-# Copyright (C) 2007 The OpenSDE Project
+# Copyright (C) 2007 - 2011 The OpenSDE Project
 #
 # More information can be found in the files COPYING and README.
 #
@@ -12,9 +12,35 @@
 # GNU General Public License can be found in the file COPYING.
 # --- SDE-COPYRIGHT-NOTE-END ---
 
+plugin_libdir="${libdir}/openvpn"
+
+plugins_enabled=''
+
+build_plugin() {
+	local plugin=$1; shift
+
+	echo "Building openvpn plugin $plugin..."
+	cd plugin/$plugin
+
+	eval $MAKE $makeopt
+	cp *.so ${root}${plugin_libdir}
+
+	cd ../..
+}
+
+build_plugins() {
+	install -d ${root}${plugin_libdir}
+	for plugin in $plugins_enabled; do 
+		build_plugin $plugin
+	done
+}
+
 # allow passwords to be read from a file
 var_append confopt ' ' "--enable-password-save"
 
+# where openvpn should search for plugins
+var_append CFLAGS ' ' "-DPLUGIN_LIBDIR${plugin_libdir}"
+
 # iproute2 support
 pkginstalled iproute2 && var_append confopt ' ' "--enable-iproute2"
 
@@ -22,3 +48,12 @@ if ! pkginstalled lzo ; then
 	var_append confopt ' ' "--disable-lzo"
 	echo_warning "LZO Compression Support disabled! (lzo package not installed)"
 fi
+
+# pam authentication plugin
+pkginstalled -f pam && var_append plugins_enabled ' ' "auth-pam"
+
+# build plugins when $plugins_enabled is not empty
+if [ ! -z "$plugins_enabled" ]; then
+	echo_warning "Enabling OpenVPN plugins: $plugins_enabled"
+	hook_add postmake 3 build_plugins
+fi