* lread.c: Fix file descriptor leaks and errno issues.

* lread.c: Fix file descriptor leaks and errno issues.

(Fload): Close some races that leaked fds or streams when 'load'
was interrupted.
(Fload, openp): Report error number of last nontrivial failure to open.
ENOENT counts as trivial.
* eval.c (do_nothing, clear_unwind_protect, set_unwind_protect_ptr):
New functions.
* fileio.c (close_file_unwind): No need to test whether FD is nonnegative,
now that the function is always called with a nonnegative arg.
* lisp.h (set_unwind_protect_ptr, set_unwind_protect_int): Remove.
All uses replaced with ...
(clear_unwind_protect, set_unwind_protect_ptr): New decls.