Support .dmg disk images as distfiles with new use_dmg option

[Rainer Müller]

Ryan Schmidt wrote:
>> BTW, as we have all these use_foo options, wouldn't it be better we
>> would have something like extract.type which can be set to one of bzip2,
>> gzip, dmg?
> 
> I was hoping nobody would bring this up. :)

Sorry for that :)

>> What happens if someone specifies "use_bzip2 yes" and also "use_dmg yes"?
> 
> If you do that, I believe the universe explodes. It is, as you rightly
> point out, a single extract type that's being selected by these various
> options.

Well, but as I thought more about it know, this is not bound to the
extract phase. Also the fetch phase constructs a filename from ${name},
${version} and the type like .tar.gz or .tar.bz2. So maybe extract.type
may be the wrong location for something like that.

[...]
> I was hoping to avoid having to send that email and thereby begin this
> discussion until after the necessary basic support for extraction from
> dmgs, as per my ticket, was committed to base.

As this also affects the extract types already in base code, I don't see
this as objection to include support for disk images right now.
We have to deal with this, but that can also be done later on.

Rainer