Use logical instead of physical path for locating WM_PROJECT_DIR

As experienced by @ivanspisso during installation, the current use of pwd -P makes the installation in some cluster environments more difficult since the physical path may correspond to some arbitrary disk and not to the canonical name. For example,

OK:  /cineca/prod/opt/applications/ 
NOK: /marconi/prod/opt/applications/
NOK: /galileo/cineca/prod/opt/applications/