INCLUDES are now deprecated and throw warnings when using automake 1.13.
We now also differentiate AM_CPPFLAGS and AM_CFLAGS, where includes and
defines are passed to AM_CPPFLAGS only.
This makes EAP-GTC a generic plain password authentication method,
as it is used with XAuth. Instead of verifying credentials with
PAM, any backend can be configured. The default is xauth-pam,
providing the same functionality as EAP-GTC in strongSwan 4.x.