Fix build for 4.3 (#524)

For some reason, the test build is failing on Linux/release. This seems
to fix it. I'm not sure why.

src/unity/lib/CMakeLists.txt

@@ -30,7 +30,7 @@ make_library(unity_core
     ../extensions/additional_sframe_utilities.cpp
     unity_sarray_builder.cpp
     unity_sframe_builder.cpp
-    ${VISUALIZATION_SOURCES}
+    visualization/columnwise_summary.cpp
   REQUIRES
     flexible_type
     pylambda 

src/unity/lib/visualization/CMakeLists.txt

@@ -1,11 +1,16 @@
 project(unity)
 
+# HACK HACK HACK
+# columnwise_summary.cpp should be in this file, not the parent directory,
+# but including it here for some reason causes linker errors
+# in release/test (C++ unit tests) - but not debug! And only on Linux.
+# Not sure why.
+
 make_library(
   visualization
   SOURCES
     boxes_and_whiskers.cpp
     categorical_heatmap.cpp
-    columnwise_summary.cpp
     escape.cpp
     groupby.cpp
     heatmap.cpp

src/unity/lib/visualization/columnwise_summary.cpp

@@ -1,4 +1,5 @@
 #include "columnwise_summary.hpp"
+#include <unity/lib/unity_sframe.hpp>
 
 namespace turi {
   namespace visualization {

src/unity/lib/visualization/columnwise_summary.hpp

@@ -14,10 +14,10 @@
 #include <unity/lib/visualization/summary_view.hpp>
 #include <unity/lib/visualization/vega_data.hpp>
 #include <unity/lib/visualization/vega_spec.hpp>
-#include <unity/lib/unity_sframe.hpp>
-#include <unity/lib/gl_sframe.hpp>
 
 namespace turi {
+  class unity_sframe_base;
+
   namespace visualization {
     std::shared_ptr<Plot> plot_columnwise_summary(
       const std::string& path_to_client, std::shared_ptr<unity_sframe_base> sf);