[Exim] new spam tagging

It seems that a new breed of spam is aroud that uses as a
$sender_address_local_part made up of twice the recipient
$local_part. Time to add a new rule:

# SENDER USERNAME = 2 x RECIPIENT acl_m5
warn    condition = ${if  eqi \
            {$sender_address_local_part}\
            {${local_part}${local_part}}\
            {yes}{no}}
         set acl_m5 = 3

Giuliano