Relative calculation of dm.php in ProjectConfiguration

Allows easy moving around of whole DIEM-Project if Diem-Root is
possibly-relative (under the tree) of project-folder...

dmFilesystem had to be created because of protected-hidden functions in
sfFilesystem.
Revert "Relative calculation of dm.php in ProjectConfiguration"

This reverts commit 94e21420daf94f2c24209a15c9861501712018e0.