restore some symbol table functions for backward compatibility These functions were removed from the public interface before being deprecated. * interpreter.h, interpreter.cc (interpreter::top_level_variable_names): New function. * pt-eval.h, pt-eval.cc (tree_evaluator::top_level_variable_names): New function. * call-stack.h, call-stack.cc (call_stack::top_level_variable_names): New function. * symtab.h, symtab.cc (symbol_table::at_top_level, symbol_table::varval, symbol_table::global_varval, symbol_table::top_level_varval, symbol_table::global_variable_names, symbol_table::top_level_variable_names, symbol_table::variable_names, symbol_table::assign, symbol_table::clear_all, symbol_table::clear_global, symbol_table::clear_global_pattern, symbol_table::clear_symbol, symbol_table::clear_symbol_pattern, symbol_table::global_assign, symbol_table::top_level_assign): New functions.

--- a/libinterp/corefcn/call-stack.cc	Wed Oct 30 15:19:07 2019 -0700
+++ b/libinterp/corefcn/call-stack.cc	Thu Oct 31 00:51:45 2019 -0400
@@ -735,11 +735,6 @@
     return m_cs[m_curr_frame]->regexp (pattern);
   }
 
-  std::list<std::string> call_stack::variable_names (void) const
-  {
-    return m_cs[m_curr_frame]->variable_names ();
-  }
-
   std::list<std::string> call_stack::global_variable_names (void) const
   {
     std::list<std::string> retval;
@@ -755,6 +750,16 @@
     return retval;
   }
 
+  std::list<std::string> call_stack::top_level_variable_names (void) const
+  {
+    return m_cs[0]->variable_names ();
+  }
+
+  std::list<std::string> call_stack::variable_names (void) const
+  {
+    return m_cs[m_curr_frame]->variable_names ();
+  }
+
   void call_stack::clear_global_variable (const std::string& name)
   {
     auto p = m_global_values.find (name);