BUG/MEDIUM: stats: stats bind-process doesn't propagate the process mask correctly

BUG/MEDIUM: stats: stats bind-process doesn't propagate the process mask correctly

With nbproc > 1, it is possible to specify on which process the stats socket
will be bound using "stats bind-process", but the behaviour was not correct,
ignoring the value in some configurations.

Example :
global
  nbproc 4
  stats bind-process 1
  stats socket /var/run/haproxy.sock

With such a configuration, all the processes will listen on the stats socket.
As a workaround, it is also possible to declare a "process" keyword on
the "stats stocket" line.

The patch must be applied to 1.7, 1.6 and 1.5