prevent seq from inflow on I/O errors

[Assaf Gordon]

Hello,

The attached patch add I/O error checking to seq, preventing infloop on certain 
write-error conditions.

The typical case is
      seq 1 inf > /dev/full

but also a more rare case is of systems with SIGPIPE set to ignore by default
(same weird system in recent grep thread: 
http://lists.gnu.org/archive/html/bug-grep/2016-03/msg00025.html ).

On that weird system, commands like 'seq 999999 inf | head -n2' would run 
forever because SIGPIPE is ignored, and seq did not check for errors. (This 
exact command is found in ./tests/misc/seq-precision.sh).

Comments and feedback welcomed,
regards,
 - assaf

0001-seq-detect-and-report-I-O-errors.patch
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