Fix timing edge cases in t_renew.py

When we are testing maximum renewable lifetimes, the KDC might process
the request at a later time than the request time (typically by no
more than one second).  So we need to ask for a ticket lifetime longer
than the maximum renewable lifetime, not equal to it, or we risk
getting a just-barely-renewable ticket instead of a non-renewable one.
Also fix a couple of typos in comments.
Add libkrad

The new library libkrad provides code for the parsing of RADIUS packets
as well as client implementation based around libverto. This library
should be considered unstable.
Add server-side otp preauth plugin

This plugin implements the proposal for providing OTP support by
proxying requests to RADIUS. Details can be found inside the
provided documentation as well as on the project page.

http://k5wiki.kerberos.org/wiki/Projects/OTPOverRADIUS