[Exim] convert4r4 buglet

Convert4r4 treats quotes as part of the argument of rbl_domains, e.g.:
rbl_domains = "relays.osirusoft.com/warn"
is interpreted as hostname '"relays.osirusoft.com' and action 'warn"'
(which is invalid, so it is ignored and the default deny action is used
instead).
Otherwise it appeared to work quite well.
Thanks,
John Dalbec