Throw an exception for possible file race condition

Currently we should uses the @-operator on mkdir(), for instance, to check
a race condition. Something like:

if (!@mkdir('test')) {
throw new SomeException();
}

Should be fine if we can do something like that, instead:

try {
mkdir('test');
}
catch (FileExistsException $exception) {
throw new SomeException();
}

It will avoid the @-operator and make the result more reliable (for
instance, if you don't uses the @-operator in this case and is catched by a
race condition).

--
David Rodrigues