MEDIUM: init: support a list of files on the command line

MEDIUM: init: support a list of files on the command line

HAProxy could already support being passed a file list on the command
line, by passing multiple times "-f" followed by a file name. People
have been complaining that it made it hard to pass file lists from init
scripts.

This patch introduces an end of arguments using the common "--" tag,
after which only file names may appear. These files are then added to
the existing list of other files specified using -f and are loaded in
their declaration order. Thus it becomes possible to do something like
this :

    haproxy -sf $(pidof haproxy) -- /etc/haproxy/global.cfg /etc/haproxy/customers/*.cfg