index buggy for matching patterns longer than 3

[John W. Eaton]

On  7-Aug-2007, Jean-Francois Cardoso wrote:

| There is an error in the logic of find.m which makes it report a
| matching pattern when *only* the first three characters match.
| For example,
|      index("abc---", "abc+++")
| returns 1 rather than 0.
| 
| The following patch fixes this and also adds the relevant new
| testcases.

I made this change.

Thanks,

jwe