Simplify error handling of tty_putc()
Simplify error handling of tty_putc()

The error handling can be done inside tty_putc() even tho it's used as
the putfunc argument to tputs() since the latter does not rely on
getting EOF back. Quoting POSIX[1]:

  The user-supplied function putfunc (specified as an argument to
  tputs()) is either putchar() or some other function with the same
  prototype. The tputs() function ignores the return value of putfunc.

[1] http://pubs.opengroup.org/onlinepubs/7908799/xcurses/putp.html

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