Display an informative message, rather than a Groovy exception, when
Don't try to set Agent Port when it is enforced, breaking form submission.
Don't add all group names as HTTP headers on "access denied" pages, possibly breaking reverse proxies due to very large headers.
Fix handling of the POST flag in
ManagementLinks within the Manage Jenkins page.
IllegalStateException from Winstone when making certain requests with access logging enabled.
Do not fail to write a log file just because something deleted the parent directory.