Allow normal lists completion also when using ido.el

Allow normal lists completion also when using ido.el

Gregory Grubbs writes:

> When exporting a table with ido-mode active, an error is
> raised in org-ido-completing-read.  I think
> ido-completing-read is being called with incorrect
> arguments, but the fix is beyond me.
>
> Steps to reproduce the error:
> Org-mode version: 6.28trans
> Emacs version: GNU Emacs 23.0.91.1 (i486-pc-linux-gnu, GTK+ Version
> 2.16.0) of 2009-04-05 on palmer, modified by Debian
>
>
> Turn on ido-mode: M-x ido-mode RET
> visit a file using C-x C-f /tmp/test.org RET
> Create a simple table:
> |column a|column b|
> |-
> |one|two|
> |three|four|
>
> Org-magic-tabelize it by hitting TAB somewhere in a column
>
> M-x org-table-export RET /tmp/test.csv
>
> Here's the backtrace I get:
>
> Debugger entered--Lisp error: (wrong-type-argument listp "orgtbl-to-tsv")

This error is due to the fact that org-ido-completing-read does
convert alists to flat lists for completion.  Now we check if the list
really is an alist before converting it.