could you please test if my little patch really allows using xdebug
together with Zend Debugger?

ATTENTION: you need to load xdebug with extension=xdebug.so and not via
zend_extension. When there is no other zend_extension xdebug will
register itself as zend_extension. If there is another zend_extension
xdebug replaces the statement_handler with a wrapper that first calls
xdebug's new statement_handler and then the one that the other
zend_extension has registered.