[jamming] Generation of two targets to the same location

[Vladimir Prus]

Hello,

jam now is quite benign toward binding several targets to the same location. 
In general, this cannot be made error. However, suppose that two targets are
bound to the same location via LOCATE variable. For me, this looks like 100%
error, and I'd like to be reported as such, or at least become warning. In 
Boost.Jam, such warning/error can be trivially added. 

Is this desire resonable? Or there are valid use cases where two targets are 
bound to the same location via LOCATE?

- Volodya