Handle compressed tars in ApplyLayer

When pulling from a registry we get a compressed tar archive, so
we need to wrap the stream in the right kind of compress reader.

Unfortunately go doesn't have an Xz decompression method, but I
don't think any docker layers use that atm anyway.
archive: Re-add XZ compression support

This shells out to the xz binary to support .tar.xz layers, as
there is no compression/xz support in go.
Move sqlite conn to graph db for cross compile support
Make Tianon the official root "Dockerfile" maintainer, since it's so hard-locked to hack changes most of the time
Use box-drawing characters in `docker images -tree`

This makes the output of `docker images -tree` look a little prettier.
Previously it displayed a combination of box-drawing characters and pipe
characters, so the lines didn't quite connect...

Before:

    └─aceb1e132fe5 Size: 487 MB (virtual 1.728 GB)
      |─c5480c55e00a Size: 44.89 MB (virtual 1.773 GB)
      | └─96c21b5e3c80 Size: 17.25 kB (virtual 1.773 GB)
      |   └─58f3f2293512 Size: 8.191 MB (virtual 1.782 GB)

After:

    └─aceb1e132fe5 Size: 487 MB (virtual 1.728 GB)
      ├─c5480c55e00a Size: 44.89 MB (virtual 1.773 GB)
      │ └─96c21b5e3c80 Size: 17.25 kB (virtual 1.773 GB)
      │   └─58f3f2293512 Size: 8.191 MB (virtual 1.782 GB)
Merge pull request #3270 from vreon/tree-box-drawing-characters

Use box-drawing characters in `docker images -tree`
Merge pull request #3275 from crosbymichael/sqlite-import

Move sqlite conn to graph db for cross compile support
Merge pull request #3277 from jpoimboe/fix-root-symlink

Move root symlink check to engine.New
Merge pull request #3274 from tianon/tianon-dockerfile

Make Tianon the official root "Dockerfile" maintainer
Add new "cross" bundle to cross-compile the Docker client for other platforms (currently just 32-bit and 64-bit OS X)
Merge pull request #3276 from tianon/cross-compile

Add new "cross" bundle to cross-compile the Docker client
Merge pull request #3243 from alexlarsson/compressed-tar

Handle compressed tars in ApplyLayer
add gosqlite to vendor.sh

Add gosqlite and its latest revision to vendor.sh so that the vendor
directory can be reliably recreated.