Added xauth-noauth plugin

This XAuth backend does not do any authentication of client credentials
but simply sends a successful XAuth status to the client, thereby
concluding the XAuth exchange.  This can be useful to fallback to basic
RSA authentication with clients that can not be configured without XAuth
authentication.

src/libcharon/Makefile.am

@@ -596,3 +596,10 @@ if MONOLITHIC
   libcharon_la_LIBADD += plugins/xauth_pam/libstrongswan-xauth-pam.la
 endif
 endif
+
+if USE_XAUTH_NOAUTH
+  SUBDIRS += plugins/xauth_noauth
+if MONOLITHIC
+  libcharon_la_LIBADD += plugins/xauth_noauth/libstrongswan-xauth-noauth.la
+endif
+endif