Blender Git Loki

Tweaks to the version string formation

Couple of things:

- No need to use string streams to format the version string,
we can do it at compile time and don't bother with anything
at runtime.

- Function declaration was wring and would have caused linking
conflicts in cases when util_version.h was included from
multiple places.

We should have an utility function to get Cycles version so
applications which are linked to Cycles dynamically can query
the version, but that can't be done as an inlined function in
header and would need to be a function properly exported to a
global symbol table (aka, be implemented in a .cpp file).