Ctrl+E should insert suggested completion and then go to end of line

(Closes #91, #932)

Currently, control-E is bound to `end-of-line`.

This patch modifes the `end-of-line` procedure so that, if it is invoked when
the cursor is at the end of a command and there is pending completion text,
it will accept the completion text and move to the end. The behavior of
`end-of-line` will not otherwise be altered.