repl: Add paste mode to friendly REPL, entered via CTRL-E.

Use CTRL-E to enter paste mode.  Prompt starts with "===" and accepts
all characters verbatim, echoing them back.  Only control characters are
CTRL-C which cancels the input and returns to normal REPL, and CTRL-D
which ends the input and executes it.  The input is executed as though
it were a file.  The input is not added to the prompt history.