clear_table_cache before each rename_column

Fixing issue #237

Not sure if this is the optimal solution, but it should work.

Author: michelgrootjans

lib/active_record/connection_adapters/sqlserver/schema_statements.rb

@@ -80,6 +80,7 @@ def change_column_default(table_name, column_name, default)
         end
 
         def rename_column(table_name, column_name, new_column_name)
+          connection.schema_cache.clear_table_cache!(table_name)
           detect_column_for! table_name, column_name
           do_execute "EXEC sp_rename '#{table_name}.#{column_name}', '#{new_column_name}', 'COLUMN'"
         end