Pattern for executing arbitrary PHP functions

Here are some example uses of the included patch:

  Call a function from a specified file  
  <call_php_func>
    <function>test_func</function>
    <arguments>
      <argument>arg1</argument>
      <argument>arg2</argument>
    </arguments>
    <filepath>/path/to/file/file.inc</filepath>
  </call_php_func>
  
  Call a function from an include file from a module
  <call_php_func>
    <function>test_func</function>
    <arguments>
      <argument>arg1</argument>
      <argument>arg2</argument>
    </arguments>
    <type>inc</type>
    <module>my_module</module>
    <name>include_name</name>
  </call_php_func>
  
  Call a function defined in a module (no need for include)
  <call_php_func><function>test_func</function></call_php_func>