While it is great for (some) streaming cases it is really wrong for saving
to a file for example and/or without using the gather module.

 If you have read how to use the gather module, you probably have read enough
documentation to add sout-keep...

This is of course NOT a good solution, and it has nothing to do in the interface...
So, either we let it like this, or we implement in the good place (not in intf)
or we remove this option

(cherry picked from commit ed98d997)

(cherry picked from commit 2b112bad)

Already available in the interface sprefs.
This reverts commit 1abb581f.

(cherry picked from commit c1a144df)

(cherry picked from commit 446be1c2)

(cherry picked from commit b7e41633)

(cherry picked from commit 9a5e5236)

(cherry picked from commit d6c0f242)

The only user is LUA, inlined there. The return value seems suspicious
by the way.
(cherry picked from commit 1014a2aa)

(cherry picked from commit be0af925)

(cherry picked from commit 475d7593)

(cherry picked from commit daf44288)

(cherry picked from commit b3bf199a)

(cherry picked from commit 674c2927)

(cherry picked from commit ebc680ce)

(cherry picked from commit 48593ea3)

(cherry picked from commit dc8228bb)

Fix make dist

Seems to work but needs more testing

(cherry picked from commit 63b5b2e2)