Merge filter settings when merging .cov files

Fixes sebastianbergmann/phpcov#18

Author: javer

src/CodeCoverage.php

@@ -370,6 +370,13 @@ public function merge(PHP_CodeCoverage $that)
         }
 
         $this->tests = array_merge($this->tests, $that->getTests());
+
+        $this->filter->setBlacklistedFiles(
+            array_merge($this->filter->getBlacklistedFiles(), $that->filter()->getBlacklistedFiles())
+        );
+        $this->filter->setWhitelistedFiles(
+            array_merge($this->filter->getWhitelistedFiles(), $that->filter()->getWhitelistedFiles())
+        );
     }
 
     /**