bug#17533: 24.4.50; Word Isearch bug

[Juri Linkov]

> From "emacs -Q":
>   f o o RET - > f o o C-s M-s w - > f o o
>
> Expected: Only the string "->foo" is matched.
>
> Observed: There are two (quite strange) matches:
> 1. From the final dot in the *scratch* buffer to the end of the first
>    "foo".
> 2. From the end of the first "foo" to the end of the second "foo".

In word search mode, non-word characters are interpreted as whitespace.