libpcp: suppress pduread EINTR warnings for interactive tools
libpcp: suppress pduread EINTR warnings for interactive tools

<myllynen> occasionally hitting Ctrl-C when running pmrep gives:
<myllynen> ^C[Tue Oct 29 13:08:39] pmrep(12023) Error: pduread: select() on fd=3 status=-4: Interrupted system call

EINTR is harmless and doesn't need that reporting - handle this
as a special case inside the pduread error path in question.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp