FIX: copying physioset files under Linux

When reproducing the processing results obtained by other users
in a Linux shared environment, trying to overwrite an already
existing physioset file which is owned by other user will trigger
an error. See:

http://www.mathworks.nl/support/solutions/en/data/1-98H2VH/index.html?product=SL&solution=1-98H2VH

This has been solved by deleting the conflicting file rather than
overwritting it.