T-Res: two tasks on the same node cannot have the same input source

[dalessan]

If two T-Res tasks on the some node have the same input source, only one of the two tasks can actually monitor the input source. Indeed, a node cannot observe the same resource twice.

This can be fixed by changing how T-Res handles input sources: T-Res should check if an input source is shared among two or more tasks and notify all of them when a new notification is received.