Events sent down each branch of a FanOut sink should be independent

Currently, if an event is sent down two paths that annotate the event, because the same instance of the event is used, there may be an unexpected attribute overwrite exception.

Examples:

[

{value("foo","bar") => console} , {value("baz", "blah") => console} ]

This would output something like:

event {foo:bar}
event {foo:bar, baz:blah}

Notice that the foo attribute is on the second event!

For this example
[ {value("foo","bar") => console}

,

{value("foo", "failure") => console}

]

The first would succeed but the second branch would fail because foo is being overwritten!