Fix a bug loading v2 lockfiles
Fix a bug loading v2 lockfiles

This commit fixes a bug in Cargo where after `DefaultBranch` and
`Branch("master")` are considered distinct no v2 lockfile would by
default match a dependency specification with the `branch = 'master'`
annotation. A feature of the v2 lockfile, however, is that no mention of
a branch is equivalent to the `master` branch.

The bug here is fixed by updating the code which registers a previous
lock file with our `PackageRegistry`. This code registers nodes, only
with v2 lock files, for both default and `master` branch git
dependencies. This way requests for either one will get matched now that
they're considered distinct.

rustyhorde/cargo,eminence/cargo,rust-lang/cargo,rustyhorde/cargo,rust-lang/cargo,eminence/cargo,rustyhorde/cargo,eminence/cargo,rust-lang/cargo,nipunn1313/cargo,eminence/cargo,rust-lang/cargo,nipunn1313/cargo,rustyhorde/cargo,nipunn1313/cargo,nipunn1313/cargo