Fix unchecked return values

Fix unchecked return values

This change fixes numerous places where the return values of various
system calls and standard library routines are not checked.  In
particular, this fixes occurrances called out when building on Ubuntu
12.10, with gcc 4.7.2 and eglibc 2.15-0ubuntu20.1, when the possible
failure is one we actually do (or should) care about.  This change
does not consider calls where the failure is one we deliberately
choose to ignore.

Reviewed-on: http://gerrit.openafs.org/9979
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 720363fa9bf7cfbebdc485104b74ca6bac1895f6)

Change-Id: I9e72a68a66d751139f7129b9b177ba18389c10a2
Reviewed-on: https://gerrit.openafs.org/12521
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>