FTP: Allow anonymous ftp without TLS even when TLS required.

Some SSL/TLS capable ftp clients (eg lftp) don't AUTH TLS for anonymous ftp.
There's no major reason to disallow this on the server side for anonymous
ftp (when enabled), so allow it.
Merge branch 'patches/bug4594' into devel

* patches/bug4594:
  FTP: Allow anonymous ftp without TLS even when TLS required.
Fixed request trace nesting inconsistency.
Perform negative caching of (typically) htaccess files for 5 seconds.

This avoids trying to stat the same files over and over in a single request.
Also added a 60 second timeout for positively cached files.