Check that a filter using the $header filter option is working as expected.
Test that a filter using the $header filter option works on an external script.
||abptestpages.org/testfiles/header/$header=content-type=application/javascript
Test that a filter using the $header filter option works on an image.
||abptestpages.org/testfiles/header/image.png$header=content-type=image/png
Test that a $header filter containing a comma (escaped as "\x2c") works on an image.
||abptestpages.org/testfiles/header/image2.png$header=date=\x2c
Test that a filter using the $header filter option works on an external stylesheet.
||abptestpages.org/testfiles/header/$header=content-type=text/css