[RFTesters] Make portable sgetn/1-in and 1-io tests

[David Edelsohn]

	This patch appears to fix the failures on AIX.

PASS: 27_io/basic_filebuf/sgetn/char/1-in.cc (test for excess errors)
PASS: 27_io/basic_filebuf/sgetn/char/1-in.cc execution test
PASS: 27_io/basic_filebuf/sgetn/char/1-io.cc (test for excess errors)
PASS: 27_io/basic_filebuf/sgetn/char/1-io.cc execution test

Thanks, David