at the beginning and end of readline (and readmultiline).

This fixes Home and End keys not working on macOS:
ruby/irb#330

We need to go into keyboard_transmit mode because only then do some
terminals (including xterm) actually send the sequences they specify in
terminfo.

We already have key bindings for the arrow keys 'kcuu1', 'kcud1', 'kcuf1', and 'kcub1'.

This hack only existed because the arrow keys key bindings weren't
working (for some terminals) because reline wasn't putting the terminal
into keypad transmit mode.

The escape sequences for 'cuu', 'cud', 'cuf', and 'cub' are not what the
terminal sends when arrow keys are pressed.  They are what you send to
the terminal to tell it to move the cursor.

It just so happens that in some terminals (well xterm at least), the
escape sequences for 'cuu', 'cud', 'cuf', and 'cub' with the "%p1%d"
part ommitted from the middle happen to result in the escape sequences
for the arrow keys in normal mode, but we don't need to rely on this
anymore.