Allow unsetting cookie attibutes by resetting to null
More consistent interface: Add "return $this" to set*() methods that didn't already have them.
Fix issue where setExpires(0) works, but $expires=0 doesn't work in the constructor. Remove redundant input checking from constrcutor in favor of that offered by the set*() methods.
Make @var docblocs more consistent for cookie attributes. Only one of specified null.
Annotate expires may be a string or an int
Add unit tests for changes SetCookie behavior
Merge branch 'hotfix/4700'

Close #4700
Merge pull request #4776 from ademarre/zf4735

Zend\Http\Header\SetCookie Allow unsetting cookie attibutes by resetting to null
Merge branch 'hotfix/4776' into develop

Forward port #4776