[macports-mgr] Dependencies and variants

[Joshua Root]

Paul Guyot wrote:
>> depends_build is for things which are needed to build the software.
>> Note: this is not only the build phase, but (in MacPorts trunk) any
>> phase involved in building the software, including fetch, extract, and
>> configure. (I think I'm remembering that right.)
> 
> AFAIK, no dependency is processed for extract and fetch. In other words,
> all ports that use fetching using git on 10.5 and fetching using svn and
> git on 10.4 just don't fetch with trace mode enabled.

Indeed, the current depends_* classes are not sufficient, and their
implementation needs work. I opened #15161 to track this. I think they
can be fixed without starting from scratch, though. :-)

- Josh