datajoint/table.py: update pandas index conversion logic per #776 discussion

Author: Chris Turner

datajoint/table.py

@@ -193,9 +193,11 @@ def insert(self, rows, replace=False, skip_duplicates=False, ignore_extra_fields
         """
 
         if isinstance(rows, pandas.DataFrame):
+            # drop 'extra' synthetic index for 1-field index case -
+            # frames with more advanced indices should be prepared by user.
             rows = rows.reset_index(
-                drop=isinstance(rows.index, pandas.RangeIndex)).to_records(
-                    index=False)
+                drop=len(rows.index.names) == 1 and not rows.index.names[0]
+            ).to_records(index=False)
 
         # prohibit direct inserts into auto-populated tables
         if not allow_direct_insert and not getattr(self, '_allow_insert', True):  # allow_insert is only used in AutoPopulate