Exclude SSI Comments (#670)

* Exclude SSI comments

Exclude Nginx & Apache Server Side Include (SSI) comments from being stripped via minification, the same way IE directives are not stripped.

Both Nginx & Apache SSI directives begin with:

<!—#

So we can just look for the # and don’t strip the comment in that case.

Nginx SSI: http://nginx.org/en/docs/http/ngx_http_ssi_module.html

Apache SSI: https://httpd.apache.org/docs/2.4/howto/ssi.html

* Add tests for Nginx/Apache SSI directives

Co-authored-by: Andrew Welch <andrew@keluli.local>

lib/Minify/HTML.php

@@ -164,7 +164,7 @@ class Minify_HTML
 
     protected function _commentCB($m)
     {
-        return (0 === strpos($m[1], '[') || false !== strpos($m[1], '<!['))
+        return (0 === strpos($m[1], '[') || false !== strpos($m[1], '<![') || 0 === strpos($m[1], '#'))
             ? $m[0]
             : '';
     }