Make texture node threaded

Quite trivial idea -- just pass tread ID to the texture sampling function.

Implemented as a TLS to avoid passing huge amount of extra contexts around.
Should be working on all platforms, but compilation test is required.

Reviewers: juicyfruit, campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D1831

source/blender/compositor/intern/COM_CPUDevice.cpp

@@ -22,6 +22,12 @@
 
 #include "COM_CPUDevice.h"
 
+CPUDevice::CPUDevice(int thread_id)
+  : Device(),
+    m_thread_id(thread_id)
+{
+}
+
 void CPUDevice::execute(WorkPackage *work)
 {
 	const unsigned int chunkNumber = work->getChunkNumber();