hgrc.5: oft-requested "hg update" hook example

convert/svn: delegate to svn bindings if HTTP probe fails convert extension tries to guess the remote repository type with HTTP probes. Unfortunately, it does not handle authentication or HTTPS handshakes, so regular svn repositories may be excluded. Instead, when a non-404 error is retrieved, we keep trying with the svn bindings. The drawback is missing svn bindings will make the conversion to fail even for non-svn targets. This can be avoided with --source.

test-rebase-newancestor: make executable