Add a buildbot with +universal for all packages

[mojca (Mojca Miklavec)]

It would be sooooooo great if packages like qt4-mac and compilers like clang-3.2 would be built with +universal along the normal variants.

I would like to request either:

• to add a keyword to portfiles to signal to builtbot the desire to build a certain package and its dependencies with +universal (useful for qt4-mac, developers could add the flag to commonly used ports and those that require longest build times)
• or simply compile all packages with +universal