When UV_OVERLAPPED_PIPE was used for the pipe passed to the child process, a
problem occurred with the standard input of the .Net Framework application
(#11809). Therefore, add the overlapped option to jobstart() and change it so
that it is set only when necessary
If an autoloaded function hasn't been resolved before it is used in
function(), the self dict will not be created which causes E725 when
calling the function. Since self isn't being used in
provider#stderr_collector, we can remove the dict attribute to
workaround the self dict bug[0].
Closes#7115
[0]: https://groups.google.com/d/msg/vim_dev/I7AXOyv-P4o/DzbyOxDHBgAJ
- Show hint only once per session.
- provider#clipboard#Call(): prevent recursion
- provider#clear_stderr(): use has_key(), because :silent! is still
captured by :redir.
closes#7184
