This fixes https://savannah.gnu.org/bugs/index.php?42189.

And also case-sensitive searches, backward searches, and searching again.

This lets users of braille displays find the selected item immediately.

This fulfills a request by Enrico Mioso.
See https://lists.gnu.org/archive/html/nano-devel/2016-09/msg00025.html.

And correct a comment: the key /does/ occur also in the tiny version.

The prompt from which the browser was invoked has already blanked it.

This fixes https://savannah.gnu.org/bugs/?48987.

This fixes https://savannah.gnu.org/bugs/?48988.

These keycodes have non-rebindable entries in the list of shortcuts, so
they will always be there -- no need for a function call to find them.

In the tiny version it would beep and report an unbound key for every
window resize.

Mentioning "GNU nano" instead of "This program" and referring to the
website instead of to a postal address.

Resetting the cutbuffer is irrelevant when 'allow_funcs' is false or
when in view mode, so do_input() can just return in those cases.

And remove a superfluous call.

The prompt has already been trimmed in do_prompt() to fit into the
available space.