Description:
------------
While using the pear Class Spreedsheet_Excel_Writer i noticed a reproduciable segmentation fault.

due to the fact pear is (to my knowledge) entirely php-code, this seems to be a bug in php itself.

I tested numberous versions of php, everywhere its the same!

It happend when trying to fill a cell with the string '@-'


Reproduce code:
---------------
<?php
require_once 'Spreadsheet/Excel/Writer.php';

// Creating a workbook
$workbook = new Spreadsheet_Excel_Writer();

// sending HTTP headers
$workbook->send('test.xls');

// Creating a worksheet
$worksheet =& $workbook->addWorksheet('Crash Demo');

// The actual data
$worksheet->write(0, 0, '@-');

// Let's send the file
$workbook->close();
?> 

Expected result:
----------------
Sending an XLS

Actual result:
--------------
Segmentation fault.