Changes

The callback return primitive should return if it could return or not

- The callbacks should run with less priority of the callback queue
handler, to detect correctly the incoming callbacks and add them to the
invocation stack. - The return callback primitive now returns true or
false if it could return or not, if false, the callback should wait
until other callback returns.

The callback return primitive should return if it could return or not

- The callbacks should run with less priority of the callback queue
handler, to detect correctly the incoming callbacks and add them to the
invocation stack. - The return callback primitive now returns true or
false if it could return or not, if false, the callback should wait
until other callback returns.

The callback return primitive should return if it could return or not

- The callbacks should run with less priority of the callback queue
handler, to detect correctly the incoming callbacks and add them to the
invocation stack. - The return callback primitive now returns true or
false if it could return or not, if false, the callback should wait
until other callback returns.