Hande E_RECOVERABLE_ERROR in test's error handler

@juliens discovered a tiny bug in atoum test's error handler : it does not correctly handle E_RECOVERABLE_ERROR if there is another error after it.

He built an example repository to reproduce the bug : https://github.com/Juliens/atoum_sandbox

To sum-up: given we have something like this:

```php
<?php
//typehint.php
namespace Test;

class Foo { public function test() { } }

class TypeHint
{
    public function foo(Foo $test) { $test->test(); }
    public function foo2(Foo $test) { }
}
```

And the test:

```php
<?php
namespace Test\tests\units;


require_once __DIR__ . '/typehint.php';
require_once __DIR__ . '/atoum/scripts/runner.php';

use \Test\TypeHint as testedClass;

class TypeHint extends \atoum\test
{    
    public function testTypeHintFail()
    {
        $class = new testedClass();        

        $this->variable($class->foo(''))->isNull();
    }
    public function testTypeHintSuccess()
    {
        $class = new testedClass();        

        $this->variable($class->foo2(''))->isNull();
    }
}
```

When we run this test, we get an output which only shows the ```FATAL ERROR``` telling us we are callin a method (```test```) on a non-object because we didn't pass the required parameter in the ```testTypeHintFail``` test method.

Fo the second one, ```testTypeHintSuccess```, the ```E_RECOVERABLE_ERROR``` is shown as expected because it's the only error in the test.

This PR changes the error handler behavior a bit so that it correctly handle ```E_RECOVERABLE_ERROR```: the handler now returns false when it gets called for this type of error, stopping the test execution and letting us see the right error message (the first raised error). 

**[EDIT: Here is a before/after snippet, perhaps it's a bit clearer]**
**Before:**
```
> There are 2 errors:
=> Test\tests\units\TypeHint::testTypeHintFail():
==> Error FATAL ERROR in /Users/jubianchi/repositories/atoum_sandbox/test.php on unknown line, generated by file /Users/jubianchi/repositories/atoum_sandbox/typehint.php on line 14:
Call to a member function test() on a non-object

=> Test\tests\units\TypeHint::testTypeHintSuccess():
==> Error E_RECOVERABLE_ERROR in /Users/jubianchi/repositories/atoum_sandbox/test.php on line 20, generated by file /Users/jubianchi/repositories/atoum_sandbox/typehint.php on line 17:
Argument 1 passed to Test\TypeHint::foo2() must be an instance of Test\Foo, string given, called in /Users/jubianchi/repositories/atoum_sandbox/test.php on line 20 and defined
```

**After:**
```
> There are 2 errors:
=> Test\tests\units\TypeHint::testTypeHintFail():
==> Error CATCHABLE FATAL ERROR in /Users/jubianchi/repositories/atoum_sandbox/test.php on unknown line, generated by file /Users/jubianchi/repositories/atoum_sandbox/typehint.php on line 12:
Argument 1 passed to Test\TypeHint::foo() must be an instance of Test\Foo, string given, called in /Users/jubianchi/repositories/atoum_sandbox/test.php on line 15 and defined

=> Test\tests\units\TypeHint::testTypeHintSuccess():
==> Error CATCHABLE FATAL ERROR in /Users/jubianchi/repositories/atoum_sandbox/test.php on unknown line, generated by file /Users/jubianchi/repositories/atoum_sandbox/typehint.php on line 17:
Argument 1 passed to Test\TypeHint::foo2() must be an instance of Test\Foo, string given, called in /Users/jubianchi/repositories/atoum_sandbox/test.php on line 20 and defined
```