This also makes the editor clean as many lines as the searching took,
for instance, in the case of <C-r><C-c>ls<tab>, two lines should be
cleaned, not just one.
Fixes#3413.
Makes C-c print "^C" and continue prompting on a new line.
Also fixes a problem where an interrupted get_line() would need more
read()'s than required to update the display.
Prior to this, no keybinding were installed on the search editor, and so
editing wasn't really possible.
Also fixes <C-r> making infinite search editors.
