Feature--user_code_plugin--Adding_aliases

This branch support the creation of aliases using the plug-in User_code. When a "datastart event" occurs, a reference is produced and is linked with the data that becomes available. Using this new aliasing feature, a new reference can be produced with the same properties than the original reference expect for the name that differs. Thus, the same data can be accessed using different names.

This feature is especially useful during transaction when the reclaim/release of data is deferred at the end of the transaction.