Remove particlegen lambda syntax.

Lambdas are not supported by older compilers.  So it doesn't make sense to
write idioms that involve them.
Refactoring: float4 -> float3 where it makes sense.
Refactor: idiomize and declutter
Refactor: more idioms.
Refactor: More idioms.  Minor numerical change...

Convert x / dot(x,x) to normalize(x), which is "better", but changes behaviour
slightly.
Refactor: break interpolation into its own function.
Refactor: cleanup variables as much as I can.
Refactor: polar to cartesian in function.
Refactor: comment changes and move no-path
Merge remote-tracking branch 'jeff/master'; commit '82e3967c12b8916d31d7a8efa48fdc77bf83b25e' into stable
Bug fix for Jeff's refactoring. Some type mismatches in interpolate kernel.