libunique external dependency for 2.25?

[Alexander Larsson <alexl redhat com>]

I just commited some nautilus code to trunk (for 2.25) that makes use of
libunique for unique application functionallity (replacing the previous
code using bonobo-activation). 

However, libunique isn't currently a blessed external dependency. So,
I'd like to propose it. (Another alternative is to put a cut-n-paste
copy in nautilus as fallback, its not a large piece of code anyway.)