Fix server error when displaying a tool with conditionals in the tool shed.

lib/galaxy/tools/parameters/basic.py

@@ -1514,8 +1514,8 @@ class DataToolParameter( ToolParameter ):
         NOTE: This is wasteful since dynamic options and dataset collection
               happens twice (here and when generating HTML). 
         """
-        # Can't look at history in workflow mode
-        if trans is None or trans.workflow_building_mode:
+        # Can't look at history in workflow mode. Tool shed has no histories.
+        if trans is None or trans.workflow_building_mode or trans.webapp.name == 'tool_shed':
             return DummyDataset()
         assert trans is not None, "DataToolParameter requires a trans"
         history = trans.get_history()

templates/webapps/tool_shed/repository/tool_form.mako

@@ -70,6 +70,8 @@
         
         <%def name="row_for_param( prefix, param, parent_state, other_values )">
             <%
+                # Disable refresh_on_change for select lists displayed in the tool shed. 
+                param.refresh_on_change = False
                 label = param.get_label()
                 if isinstance( param, DataToolParameter ) or isinstance( param, ColumnListParameter ) or isinstance( param, GenomeBuildParameter ):
                     field = SelectField( param.name )