Alembic: not using global in unit test.

Thanks @sergey for pointing out this fix.

tests/gtests/alembic/abc_export_test.cc

@@ -5,8 +5,8 @@
 #include "intern/abc_exporter.h"
 
 extern "C" {
-#include "BKE_global.h"
 #include "BLI_utildefines.h"
+#include "BKE_library.h"
 #include "BLI_math.h"
 #include "DNA_scene_types.h"
 }
@@ -37,6 +37,7 @@ protected:
 	ExportSettings settings;
 	Scene scene;
 	TestableAbcExporter *exporter;
+	Main *bmain;
 
 	virtual void SetUp()
 	{
@@ -47,18 +48,21 @@ protected:
 		scene.r.frs_sec = 50;
 		scene.r.frs_sec_base = 2;
 
+		bmain = BKE_main_new();
+
 		exporter = NULL;
 	}
 
 	virtual void TearDown()
 	{
+		BKE_main_free(bmain);
 		delete exporter;
 	}
 
 	// Call after setting up the settings.
 	void createExporter()
 	{
-		exporter = new TestableAbcExporter(G.main, &scene, "somefile.abc", settings);
+		exporter = new TestableAbcExporter(bmain, &scene, "somefile.abc", settings);
 	}
 };