bugfix: lib/sh/local.sh: add a manual errexit for $() exprs by embedding them in just a var assignment (without local or declare), whose exit status will then equal the of the $(). a `|| return` also needs to be added because errexit does not work on assignment statements. this commit adds them for func_loc(), echo_func(), canon_rel_path(), set_paths(), save_cache, cached realpath(), local.sh global vars