Fix an ages-old bug in sed(1), which resulted in the absolutely valid substitution expressions in the form `s,[fooexp],[barexp],;...' treated as invalid when the third `,' is (_POSIX2_LINE_MAX * N)-th character in the line.
Fix an ages-old bug in sed(1), which resulted in the absolutely valid
substitution expressions in the form `s,[fooexp],[barexp],;...' treated
as invalid when the third `,' is (_POSIX2_LINE_MAX * N)-th character in
the line.

MFC after:	2 weeks

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