Import less-443.

Import less-443.

* Change search behavior such that when a search is given an explicit
  pattern, the entire displayed screen is included in the search and
  not just the portion after the target line.

* Add -A option to change search behavior to the old way: only
  the portion of the screen after the target line is searched.

* Add %F formatting to prompt strings, replaced by the last component
  of the input file.

* Control-G while editing a command exits the command.

* Less now exits with status 2 if control-C is pressed and -K is in effect.

* Fix "ungetc overflow" when passing long commands via the -p option.

* Fix bug in using line filtering via the & command
  in combination with -i and -I.

* Fix bug in handling negative arguments to the -j option.

* Fix bug in handling %t in prompt strings.

* Improve handling of long option names.

* Improve percentage calculation for very large files.