[+BUGFIX] FLOW3 (Cache): Work around PHP __halt_compiler() namespaces bug
The PhpFrontend added a __halt_compiler() instruction to the end of each
cache file to ignore following meta data needed by the cache framework.
This resulted in wrong namespace scopes for certain - originally global -
Instead of __halt_compiler() we now use a simple "#" comment which should
work equally fine with the current kind of metadata we are using.