ZF-9032: Zend_Validate_Digits error text grammar can be improved


The default text of Zend_Validate_Digits when validation isn't passed is the following:

* '500.00' contains not only digit characters

An improvement might be something like:

* '500.00' contains characters that are not digits; only digits are allowed


Includes enhancement and associated tests verified with "phpunit --testdox".

Implemented with r21118

I've updated the patch against trunk as the english grammar was still a little odd. Please review.


Fixed with r21136