In order for this to work, dtsession must be setuid root. If
dtsession is not setuid root, then locking will be disabled, and a
message will be written to ~/.dt/errorlog with the message: "Unable to
lock display due to security restrictions".
Added proper SharedDtSvcReqs in lnxLib.tmpl and CplusplusLibC in
linux.cf. This allows the libstdc++ dependancy to be properly
declared for libDtSvc so that it is not neccessary to hardcode 'CCLINK
= g++' in the Imakefiles of programs linking angainst libDtSvc.