php*-vld: Logic Dumper hooks into the Zend Engine, dumps all the opcodes

The Vulcan Logic Dumper hooks into the Zend Engine and dumps all the
opcodes (execution units) of a script. It can be used to see what is
going on in the Zend Engine.

This is an extension for advanced users and can not be used to
un-encode PHP code that has been encoded with any encoder. If you can't
make it work then this tool is not for you. If you are certain there is
a bug, then please provide a patch (or a good bug report).

Site: http://derickrethans.nl/projects.html#vld
Source code: http://pecl.php.net/package/vld
Example: http://fabien.potencier.org/article/8/print-vs-echo-which-one-is-faster

```bash
// print.php
<?php print 'foo';
 
// echo.php
<?php echo 'foo';

$ php -d vld.active=1 print.php
number of ops:  4
compiled vars:  none
line     #  op                           fetch          ext  return  operands
-------------------------------------------------------------------------------
   1     0  PRINT                                            ~0      'foo'
         1  FREE                                                     ~0
   2     2  RETURN                                                   1
         3* ZEND_HANDLE_EXCEPTION                                    

$ php -d vld.active=1 echo.php
number of ops:  3
compiled vars:  none
line     #  op                           fetch          ext  return  operands
-------------------------------------------------------------------------------
   1     0  ECHO                                                     'foo'
   2     1  RETURN                                                   1
         2* ZEND_HANDLE_EXCEPTION                                    
```