Fix #0017605: Regression issue with upgrade step 184

Background and comments / rational on this commit are in http://www.mantisbt.org/bugs/view.php?id=17605.
We could add a separate heading - although for the rest of the file, we've not added /** */ blocks.

The reason I felt it would be sensible to locate it near to MANTIS_VERSION, is such that our internal version variables are all located in the same area. 

I'd probably rather change the block to:

/** DO NOT TOUCH THIS **/
define MANTIS_VERSION
define FILTER_VERISON
/** END **/