Standalone C++ v2.0 driver doesn't compile

The inclusion of the files mongo/db/security_common.cpp and mongo/db/security_commands.cpp breaks the standalone C++ driver build (can't link due to missing method definition for getUserObj). By inspection, removing the files from the source tree fixes the build; and at least the authTest and clientTest programs appear to work properly, but I don't know if that's the correct fix.

Anyway, this effects the core server, since either the SConstruct files or the security*.cpp files need to be reorganized to compile the standalone driver.