Fix table formula bug with negative result numbers

Fix table formula bug with negative result numbers

Willian Henney writes:

> The following is using today's git trunk of org-mode with emacs
> 23.1.94.1 (aquamacs 2.0preview5)
>
>    Consider the following table
>
>    | -8 |
>    |    |
>    |    |
>    |    |
> #+TBLFM: $1=@-1 - 1::@1$1=-8
>
>    Evaluate formulas once (C-u C-c *):
>
>    | -8 |
>    | -9 |
>    |----|
>    | -1 |
>
>    Evaluate formulas again (C-u C-c *):
>
>    | -8 |
>    | -9 |
>    |----|
>    |----|
>
>    What I expected:
>
>    |  -8 |
>    |  -9 |
>    | -10 |
>    | -11 |
>
> The problem always seems to start at -10. When I turn on table
> debugging, it first calculates the -10 value correctly, but then fails
> to recognise the -10 cell as a number when calculating the next row,
> using 0 instead, which results in -1. This is because during the
> intermediate formatting of the cell the minus sign in -10 abuts the
> column separator: "|-10 |", and the "|-" part is then interpreted as
> the beginning of an hline.