Add expectedCount to toString return value

Previously when using `assertThat` with `logicalOr` and one of the constraints was `PHPUnit_Framework_Constraint_Count`, the error message was without values (count is greater than  or count matches .)
Merge pull request #1528 from koenpunt/count-to-string-value

Add expectedCount to toString return value
Merge branch '4.4' into 4.5