Replace DEFINER in database dump

[adam-paterson]

Database dumps with store procedures or triggers contain their definer. When importing to another database where the definers might vary it causes issues. netz98/n98-magerun#130 tackled the issue by piping a stream edit and replacing the definer statements with a wildcard.

We could look into doing the same. How it's currently implemented and for performance reasons we'll probably need to look at using the native stream_filter functions and preg_replace the definer statements.