[Dev] Parabola-friendly implementation of VCS urls for PKGBUILDs

[Luke T.Shumaker]

A while back I started working on a feature to add VCS url
capabilities to makepkg, based on a whitepaper I published on this
list.

https://gitorious.org/parabola/pacman/commits/lukeshu-fix

Shortly after I began, the upstream pacman devs started working on a
similar feature. Their implementation contains good code--ideally I'd
replace my download_$VCS() methods with theirs (we even chose the same
function names, how 'bout that!).

However, the general design of our implementations differ. I made
minimal modifications to makepkg itself, and added an external
`vcsget` tool that spits out tarballs. I believe that mine is better
design.

This is not the important part; their design does not allow for
checking source integrity--an important requirement for Parabola.

So, it'd be awesome if you guys would test my version. It's available
as 'pacman-lukeshu' from the [~lukeshu] repo.

~ Luke Shumaker