Replace pnmpaste of world file (which output result in a copy) with a custom in file replacement
(no copy, no need to reread full file on each iteration).
1G world file are now feasible with reasonable run time.
git-svn-id: svn://svn.code.sf.net/p/crossfire/code/maps/trunk@8055 282e977c-c81d-0410-88c4-b93c2d0d6712