Bug#369401: openssh-client: SenvEnv misses possibility to reset/override/disable previous settings

Hi!

According to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=573316 
this has been closed thanks to a `-` prefix, like:

     SendEnv -LANG

This is documented in manpage:

     $ man ssh_config | grep -A1 'clear previously set SendEnv'
                It is possible to clear previously set SendEnv variable 
names by prefixing patterns with  -.   The  de‐
                fault is not to send any environment variables.

But it looks like it does not works:

     $ cat ~/.ssh/config
     SendEnv -LANG -LC_ALL

     $ ssh -vvv mdk@test-machine env 2>&1 | grep LC_ALL
     debug1: channel 0: setting env LC_ALL = "fr_FR.UTF-8"
     bash: warning: setlocale: LC_ALL: cannot change locale (fr_FR.UTF-8)
     LC_ALL=fr_FR.UTF-8

Bests,

-- 
[Julien Palard](https://mdk.fr)