Ideally, we would just use "golint ./..." to check all our our source
files for lint error. However, this does not work because it will
include all packages in the vendor directory. The pull request at:
	https://github.com/golang/lint/pull/325
fixes this issue, so we will use it until the PR has been merged.

This change ot Gopkg.toml will make it easier to build the linting and
formatting tools. Vendoring their source also makes sure that updates to
these tools do not break the build.

fscrypt directly depends on 5 repositories (8 packages). This change
adds those dependancies to Gopkg.toml, so that they can be properly
versioned. Note that the golang.org/x repositories do not use semver.

This change transitions to dep, sets up Gopkg.toml, and purnes the
maximum allowable number of files.