Replace most of the remaining stdio calls by estream calls.
We need to use es_fopen on Windows to cope with non-ascii file names.
This is quite a large but fortunately straightforward change. At a
very few places we keep using stdio (for example due to the use of
popen).
- GnuPG-bug-id: T5098
- Signed-off-by: Werner Koch <wk@gnupg.org>