Remove references to svnbook-dev@ mailing list from the website
* www/index.it.html
Remove links to the mailing list information
Externals lines starting with '#' are ignored
Committed to trunk/en; backported to branches/1.7/en.
Merge from ^/trunk/en r6061.
Issue #284: Document the externals definitions comment syntax.
* ch03-advanced-topics.xml