setterm: correct usage() bright color argument

This has been wrong since commit 2dc8716.  The bright is a prefix
attribute to other colors.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: improve perform_sequence() coding style

Delete pointless braces, new lines, and add spacing between operators.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: tell user when options does not effect

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: improve error messages

Reuse messages to make translation work easier.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: various visual terminal effects are not console specific

Setting colors, making line not to wrap, and so on can be attempted in
other than consoles.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: mark some options to be exclusive with each other

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
setterm: add set_blanking() action

This make over long perform_sequence() function a little bit shorter.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>