The copyright and license notice is already in the LICENSE file. There
is no justifiable reason to also require that it be included in every
file, since the individual files are not individually distributed except
as part of the entire package.
Don't execute the callback in the context of the global object.
MakeCallback() tries to apply the active domain to the callback. If the user
polluted the global object with a 'domain' property, as in the code example
below, MakeCallback() will try to apply that.
Example:
domain = {}; // missing var keyword is intentional
crypto.randomBytes(8, cb); // TypeError: undefined is not a function
Fixes#3956.