Lamps were not tagged with `ID_RECALC_SHADING` when they were updated
from drivers. As a result, Cycles considered the lamp as unchanged. This
is resolved by having a (seemingly non-functional) callback in a new
`LIGHT_UPDATE` depsgraph node.
This patch unconditionally adds the `LIGHT_UPDATE` node + the relation
from the lamp's PARAMETERS node.
Differential Revision: https://developer.blender.org/D7822
Reviewed by: brecht
Surrounding includes with an 'extern "C"' block is not necessary anymore.
Also that made it harder to add any C++ code to some headers, or include headers
that have "optional" C++ code like `MEM_guardedalloc.h`.
I tested compilation on linux and windows (and got help from @LazyDodo).
If this still breaks compilation due to some linker error, the header containing
the symbol in question is probably missing an 'extern "C"' block.
Differential Revision: https://developer.blender.org/D7653
Instead of using anonymous booleans flags, also allows to keep the same
behavior in all cases, without needing special handling from calling
code for our beloved oddballs object proxies...
