ykclient 2.6

[Simon Josefsson]

Get it from:
https://code.google.com/p/yubico-c-client/downloads/list

/Simon

* Version 2.6 (released 2011-06-06)

** Use fprintf+exit instead of glibc-ism errx.
Reported by Jussi Sallinen <ju...@jus.si>.

** Indent code and replace // comments with /* */ comments (for C89).

** Fix dates of releases for 2.4 and 2.5 below (2011 not 2010).