Merge branch 'refs/heads/t/strerror'

Was cooking in next since 2015-09-27.

* refs/heads/t/strerror:
  error.h: Never call (para_)strerror() on osl errors.
  Clarify para_strerror().
  error.h: Remove is_errno().

diff --cc afs.c
Simple merge

diff --cc error.h
Simple merge