less misbehaves when stdin is a not a tty

[Garrett D'Amore]

less misguesses terminal size when stdin is a pipe. This shows up for example with man.

Problem is setupterm() is using stdin to check tty state. Better to use stdout. :-)

[Garrett D'Amore]

fixes #86 less misbehaves when stdin is a not a tty

→ <<cset a08170b953c4>>