Implemented the RFC `Catchable "Call to a member function bar()..."`

This pull request supersedes php/php-src#647 and has all commits from there squashed into one big one, including a `NEWS` entry.

* * * 
This turns fatal errors generated from calls to methods on a non-object into E_RECOVERABLE_ERRORs.

## Example

```php
set_error_handler(function($code, $message) {
  var_dump($code, $message);
});

$x= null;
var_dump($x->method());
echo "Alive\n";
```

The above produces the following output:

```
int(4096)
string(50) "Call to a member function method() on a non-object"
NULL
Alive
```

For details see https://wiki.php.net/rfc/catchable-call-to-member-of-non-object