read return from strerror_r to appease GCC 4.8

Signed-off-by: Sean Ogden <positivelyskewed.sf@gmail.com>
Merge branch 'fix_warnings' of git://github.com/seanogden/po6

* 'fix_warnings' of git://github.com/seanogden/po6:
  read return from strerror_r to appease GCC 4.8