adding canonical proc for instantiating and mounting a package: site_node::instantiate_and_mount. Deprecatating old procs with this functionality and making them invoke the new proc. Adding after-mount callback invocation in site_node::mount. Adding warn flag to a few deprecated site-node related procs.
adding support for Tcl proc package callbacks. Currently only supporting after-install and after-instantiate callbacks (next up is after-mount). There is no UI yet.