Re: defvar -> defcustom

[Richard Stallman]

    M-x customize-variable already does some guessing based on the
    variable name, so some sort of minimal guessing might be possible.
    Current conventions would also allow to search backwards from the
    defvar to the closest preceding defgroup and just assume it.

You can give it a try if you want.  But these heuristics are not
reliable.  For instance, many variables whose names suggest a value
of t or nil in fact allow other values too.  The only way to tell
is to understand the doc string.

Weighing the time that manual editing takes against the importance of
getting the right answer, and considering that this conversion only
needs to be done once in a while, I think doing it manually may be
better.