Revert "Always configure the pipeline_loader instead of custom_loader…

… when choosing a loader, since the latter is always None (fixes stefan-jansen#218)"

This reverts commit 8165deb.

src/zipline/utils/run_algo.py

@@ -176,8 +176,13 @@ def _run(
         bundle_data.adjustment_reader,
     )
 
-    def choose_loader(_column):
-        return pipeline_loader
+    def choose_loader(column):
+        if column in USEquityPricing.columns:
+            return pipeline_loader
+        try:
+            return custom_loader.get(column)
+        except KeyError:
+            raise ValueError("No PipelineLoader registered for column %s." % column)
 
     if isinstance(metrics_set, str):
         try: