Proposed change to xorgcfg

[Kean Johnston]

> A much better solution would be to have an extra option (which defaults to 
> yes when omitted) like 'option autoprobeFrequencies'.
That was exactly what I proposed in my original mail, except I
used a slightly less verbose keyword 'UseDDC' or somesuch.

So what I had in mind was:
if (UseDDC is set AND we got DDC ranges)
  use DDC probed ranges
else
  if ranges specified in the config file
    use those ranges
  else
    fall back to some pesimistic defaults
  endif
endif

Kean