Fix#29475: remove node from properties editor crash on windows. This was a bug
in the UI code, which code access removed data.
Fix OpenCL still being used in a case where Experimental was disabled.
Fix msvc debug warning in md5 code.
* Compute MD5 hash to deal with nvidia opencl compiler cache not recognizing
changes in #included files, makes it possible to do kernel compile only
once and remember it for the next time blender is started.
* Kernel tweak to compile with ATI/linux. Enabling any more functionality than
simple clay render still chokes the compiler though, without a specific error
message ..