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).

Backported-from-master: 390497ea115e1aca93feec297a5bd6ae7b1ba6dd

• GnuPG-bug-id: T5098
• Signed-off-by: Werner Koch <wk@gnupg.org>