Add support for Alien::Build installs

[plicease]

This PR is baby steps in making progress on #157

What this does:

• Adds support for Alien dists installed via Alien::Build
• Adds a dependency on Test2, which I am using in Alien::Build. I beleive the benefits outweigh the negatives.
• Adds support for static flags via cflags_static and libs_static
• Load Alien::Base::PkgConfig as needed, rather than always
• Removes support for Alien::Builder, which was never actually used
• Renames _keyword to _pkgconfig_keyword to make it clear that it is specific to pkgconfig stuff
• Rename undocumented pkgconfig to _pkgconfig to mark it as private and discourage external use. (I am pretty sure it is not used anywhere outside of this class anyway).

What this does not do:

• add any new configure or runtime dependencies
• merge Alien::Build + Alien::Base into Alien-Base, though that is my longer term goal
• remove Alien::Base::ModuleBuild from Alien-Base, though my longer term goal is to spin AB::MB into Alien-Base-ModuleBuild
• break any existing Alien's that are using AB::MB

In terms of reliability, these modules are already using Alien::Build (installtime) + Alien::Base (runtime):

http://matrix.cpantesters.org/?dist=Alien-curl+0.02
http://matrix.cpantesters.org/?dist=Alien-nasm+0.14
http://matrix.cpantesters.org/?dist=Alien-Libbz2+0.18
http://fast-matrix.cpantesters.org/?dist=Acme-Alien-DontPanic2%200.0500
http://fast-matrix.cpantesters.org/?dist=Acme-Ford-Prefect2%200.0500

In terms of Why? I would like to start migrating more Aliens to use Alien::Build and writing wholly new Aliens, and to do this I need support in Alien::Base.