Solution to bug #3080 Hash::flatten endless loop

Probably closes ticket #3080 in CakePHP Lighthouse (http://cakephp.lighthouseapp.com/projects/42648/tickets/3080-hashflatten-endless-loop-on-single-0-int-keys).
Hash::flatten has a bug which causes an endless loop when try to flatten an integer key.
Probably the $data array pointer won't reset itself when doing:
```php
$data = $element
```
and
```php
list($data, $path) = array_pop($stack)
```
The solution is to reset the pointer after the assignments.

You can test the error with the following array:
<pre>
2013-01-08 11:41:39 Debug: Array
	(
	    [AteAccountLogin] => Array
		(
		    [id] => 68
		    [username] => test
		    [is_active] => 0
		    [created] => 2012-12-17 09:40:10
		    [modified] => 2012-12-17 09:40:10
		)

	    [AteAccountProfile] => Array
		(
		    [id] => 90
		    [email] => test
		    [phone] => +39 340 0707596
		    [login_id] => 68
		    [type] => P
		    [company] => None
		    [name] => Marco
		    [surname] => Tisi
		    [country_id] => 109
		    [cf] => FAKECF
		    [vat] => 012456874
		    [cap] => 35030
		    [city] => Rovolon
		    [address] => Via Mazzini 2/B
		    [province] => Padova
		    [tos] => 1
		    [created] => 2012-12-17 09:40:10
		    [modified] => 2013-01-07 16:18:45
		    [Country] => Array
		        (
		            [id] => 109
		            [iso2] => IT
		            [name] => Italy
		            [long_name] => Italian Republic
		            [iso3] => ITA
		            [numcode] => 380
		            [un_member] => yes
		            [calling_code] => 39
		            [cctld] => .jm
		        )

		    [AteAccountAddress] => Array
		        (
		            [0] => Array
		                (
		                    [id] => 7
		                    [profile_id] => 90
		                    [country_id] => 109
		                    [cap] => 35030
		                    [city] => Rovolon
		                    [address] => Via Mazzini 32/B
		                    [province] => Padova
		                    [created] => 2012-12-20 12:56:49
		                    [modified] => 2013-01-07 16:52:56
		                    [Country] => Array
		                        (
		                            [id] => 109
		                            [iso2] => IT
		                            [name] => Italy
		                            [long_name] => Italian Republic
		                            [iso3] => ITA
		                            [numcode] => 380
		                            [un_member] => yes
		                            [calling_code] => 39
		                            [cctld] => .jm
		                        )

		                    [address_string] => Via Mazzini 32/B - 35030 - Rovolon - Padova - Italy
		                )

		            [1] => Array
		                (
		                    [id] => 14
		                    [profile_id] => 90
		                    [country_id] => 109
		                    [cap] => 35030
		                    [city] => Mestrino
		                    [address] => Test
		                    [province] => Padova
		                    [created] => 2013-01-07 17:03:11
		                    [modified] => 2013-01-07 17:03:11
		                    [Country] => Array
		                        (
		                            [id] => 109
		                            [iso2] => IT
		                            [name] => Italy
		                            [long_name] => Italian Republic
		                            [iso3] => ITA
		                            [numcode] => 380
		                            [un_member] => yes
		                            [calling_code] => 39
		                            [cctld] => .jm
		                        )

		                    [address_string] => Test - 35030 - Mestrino - Padova - Italy
		                )

		        )

		)

	)
</pre>

The endless loop starts when parsing 'AteAccountAddress' key, but if I try to isolate only that children, the bug won't appear.
I tested this with 

PHP 5.4.6-1ubuntu1.1 (cli) (built: Nov 15 2012 01:18:34) 

and 

Server version: Apache/2.2.22 (Ubuntu)