[RADIATOR] Documentation fix: %x and %X special characters

[Heikki Vatiainen]

Looks like special characters %x and %X are not in the documentation PDF
yet. These are useful for loggin the real identity of e.g., PEAP and
TTLS users.

>From 4.0 change log:
Added new special character %X, which is replaced by the EAP identity,
with any trailing @realm stripped off.

>From 3.14 change log:
Added new special character %x, which is replaced by the EAP Identity
for PEAP and TTLS inner requests.

-- 
Heikki Vatiainen, Arch Red Oy
+358 44 087 6547