[FEATURE] Enable use of @ (shut-up-operator)
By default, FLOW3 makes sure to convert any error into an exception
so that even notices don't go undiscovered.
But foreign code is not always clean and so E_NOTICE or E_STRICT
are quite common. If one doesn't want to deactivate this kinds of errors
generally the @-Operator is the only way to temporarily disable
This patch allows the error-handler to return immediately if it
detects that the parent function made use of the shut-up