Add -Wshadow to Makefile and fix the resulting warnings. Many of

Add -Wshadow to Makefile and fix the resulting warnings.  Many of
the warnings are due to the use of globals with generic names,
specifically "options" and "path".  I've renamed "options" to
"sh_options" since it holds the shell options and "path" to
"search_path".  OK jca@ tb@