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.h	Wed Oct 30 15:19:07 2019 -0700
+++ b/libinterp/corefcn/call-stack.h	Thu Oct 31 00:51:45 2019 -0400
@@ -261,9 +261,11 @@
 
     std::list<symbol_record> regexp (const std::string& pattern) const;
 
-    std::list<std::string> variable_names (void) const;
+    std::list<std::string> global_variable_names (void) const;
 
-    std::list<std::string> global_variable_names (void) const;
+    std::list<std::string> top_level_variable_names (void) const;
+
+    std::list<std::string> variable_names (void) const;
 
     void clear_global_variable (const std::string& name);