Make TestCase::hasOutput() return true if "0" is outputted

TestCase::hasOutput() returns false when "0" is outputted, as it uses empty(), which returns false on the string "0".
Merge pull request #922 from dave1010/3.7
Revert "Sync with 19f1d74."

This reverts commit f3dc675fbc6670ed6335f898efd07a4b25f04697.
Revert "Sync with API change in PHP_CodeCoverage 1.2.10"

This reverts commit 19f1d742e0c36150001062f592c93f80aef3a9fd.
Upgrade PHP_CodeCoverage
Prepare release
Merge branch '3.7'
Revert "Revert "Sync with API change in PHP_CodeCoverage 1.2.10""

This reverts commit fdf112c62f9a882f1c66ead6576eb011013d081a.