This is part XXXV of cmd engine rewrite.
It : - fixes a regression introduced by previous serie, - fixed a couple of erroneous settings of some env variables (likely corner cases)
But mostly, it's the start of implementing a pipe (between commands) as a pipe (IPC).
Currently, cmd runs lhs of pipe, stores output into a file, then runs rhs with that file as input.
However, this will expose a bunch of issues to be fixed before thinking implementing the IPC part.
This serie covers the output part: - don't filter the stderr output in the paging (MORE) output, - send all stdout output to the paging (MORE), - use a line-buffered output for stdout, - adding some explicit flush before expecting input.
It also fixes an issue triggered down the road.
Next series (likely two) will cover the input part.