add check for running as root
this is neccessary because tags of directories in dcache are owned
by root and cannot be set by another user, not even the owner of the
directory. Writing in a directory with no correctly set tags may
cause dcache to hang.
Make some smaller changes to original version to make commands
safe against spaces in filenames.
Change ls -l call to determine file size to use of stat.
make call to datasetPut space save
filterDeleted now creates an answer file containing an error message
add pid in .lock directory
make creation of answers more DRY