Don't allow user created symbolic links to cover another entries marked with DE_USER. If a devfs rule hid such entry, it was possible to create infinite number of symbolic links with the same name.
Don't allow user created symbolic links to cover another entries marked
with DE_USER. If a devfs rule hid such entry, it was possible to create
infinite number of symbolic links with the same name.

Reviewed by:	kib

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase