version.Current must die

[Tim Penhey]

Hi there,

Subject line says it all.

version.Current leads to the standard "it works on my machine".

version.Current represents the current release and architecture of the
machine that the code is running on, and probably not what we want at all.

I propose we have a version.Default() that returns a new instance of a
version.Binary that represents the current supported LTS (currently
"precise") on a 64bit OS ("amd64").

I have a branch where I have started this work, but it needs some more
time to think around the upgrade code.

Even just changing the values in version.Current to "precise" and
"amd64" causes all tests to pass except for the one that checks that
version.Current.Series is the same as `lsb-release`.

By having a defined versions.Default(), we are testing the same code on
everyone's machine.

Comments?
Tim