I've managed to move our old mediator code for use in XSLT's to the new 2013 setup, with a
<?XsltMediator extensionsTbbId="tcm:193-34-2048"?>
inside our existing XSLT template building blocks and I can successfully call C# code from within the XSLT's.
I'm wondering however, if the relationship between the .NET assembly TBB and the XSLT TBB is managed in any way in Tridion. If I do a 'Where Used' on the .NET assembly TBB, the XSLT's do not show up. We'll also be content porting our migrated code to other servers lateron and I was assuming the URI will be resolved successfully during import.
<xsl:include>
statements are managed inside Tridion, is this the same for Mediator TBB's in Tridion 2013?
UPDATE:
this indeed seems to be a defect in the 2013 product. Tridion is working on a hotfix at the moment. will update this issue once I know more....