util-lib: get_current_dir_name() can return errors other than ENOMEM

util-lib: get_current_dir_name() can return errors other than ENOMEM

get_current_dir_name() can return a variety of errors, not just ENOMEM,
hence don't blindly turn its errors to ENOMEM, but return correct errors
in path_make_absolute_cwd().

This trickles down into a couple of other functions, some of which
receive unrelated minor fixes too with this commit.