MFC r308432, r308657: Capsicumize some trivial stdio programs

r308432: Capsicumize some trivial stdio programs

Trivially capsicumize some simple programs that just interact with
stdio. This list of programs uses 'pledge("stdio")' in OpenBSD.

r308657: fold(1): Revert incorrect r308432

As Jean-Sébastien notes, fold(1) requires handling argv-supplied files. That
will require a slightly more sophisticated approach.