kakapo-lc: simplify
kakapo-lw-search: better catch/throw tag name
kakapo-open: improve error message
kakapo-lw-search: do not use catch/throw

We use a plain `while` loop with `progn` to seearch. This is simpler
than using a catch/throw mechanism. Also, explain the reasoning behind
using `(point-max)' (instead of something like

    (progn
        (forward-line 1)
        (line-beginning-position)
        (point)
    )
.
kakpo-ret-and-indent: error-checking and better behavior

Apart from error-checking, we also do not introduce any trailing
whitespace when we call this function consecutively (which may happen if
the user presses ENTER two or more times in a row).