improve handling of global symbols (bug #53599) * load-save.cc (install_loaded_variable): For global values, check global status and link to global symbol if needed. * symrec.h (symbol_record::symbol_record_rep::unbind_global_rep): New function. (symbol_record::symbol_record_rep::clear): Use unbind_global_rep to clearing global symbols. (symbol_record::symbol_record_rep::is_marked_global): New function. (symbol_record::symbol_record_rep::is_global): Use it. (symbol_record::symbol_record_rep::bind_fwd_rep): Don't forward again if symbol is already global. (symbol_record::unbind_fwd_rep): Eliminate argument. Change all uses. (symbol_record::symbol_record_rep::unbind_fwd_rep): Eliminate argument. Simplify. * test/bug-53599.tst: New file. * test/module.mk: Update.

--- a/test/module.mk	Tue Apr 10 08:39:24 2018 +0200
+++ b/test/module.mk	Tue Apr 10 22:22:37 2018 -0400
@@ -12,6 +12,7 @@
   %reldir%/bug-38576.tst \
   %reldir%/bug-46330.tst \
   %reldir%/bug-49904.tst \
+  %reldir%/bug-53599.tst \
   %reldir%/colormaps.tst \
   %reldir%/command.tst \
   %reldir%/complex.tst \