Ignore return values harder

Ignore return values harder

In various places where we intentionally ignore the return values of system
calls and standard library routines, this changes the way in which we do so,
to avoid compiler warnings when building on Ubuntu 12.10, with gcc 4.7.2 and
eglibc 2.15-0ubuntu20.1.

Change-Id: I41f806a686d68b02aec2847886bd5d787cbff3d3
Reviewed-on: http://gerrit.openafs.org/9980
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>