Protocol Cache: Assume that vary is supported by all.

This change is to avoid the vary header on User-Agent, which was
generated by the CookieJar.

Removes the workaround for MSIE 6 having broken support for vary.
Merge branch 'patches/vary' into devel

* patches/vary:
  Protocol Cache: Assume that vary is supported by all.
Version bumped to 6.0.8 by buildsystem.