Add stdmsg (an alias to either stdout or stderr).
write exception tracebacks to stdmsg, instead of stdout
Rework CGI error reporting.

- remove 'undocumented' stackTraceNL
- add 'undocumented' errorMessageWriter
- make printing errors for browser optional (for security)
Add two CGI example and basic Python CGI server.
add info about CGI error reporing changes to web/news.txt
Merge pull request #759 from zielmicha/stdmsg

Write tracebacks to stderr instead of stdout.