[dtp-connect-dev] Updated Base Content Extension Impl's

[rcernich@xxxxxxxxxx]

Hey all,

I updated the ManagedContentExtensionBase class to use the new managed
connection APIs.  I also updated the SQL model content extension to use the
managed connection.

In addition, I undeprecated (is that a word?) IContentExtension.isVisible()
and added support for using it into CommonContentProviderBase (btw, I also
updated the SQL model content extension isVisible() to return false, which
will remove the content extension node from the DSE).

Regards,
Rob