Errant edge to krate node

[nikomatsakis]

I noticed when checking the syntex-syntax node that, when I add a private fn into the crate module, it invalidates the krate-0 module. This is because the metadata includes edges to the immediate children. This seems bad, but then there is also a read whenever we read an inlined item from crate X of the crate root, which means that this winds up triggering bad reuse. I am trying to figure out why this read arises and remove it, but I'd also like to remove the dependency of metadata.

[michaelwoerister]

Was this fixed by c6363b8?

[nikomatsakis]

@michaelwoerister quite likely; I guess I will make a perf test to check

[nikomatsakis]

Looks good. Posted a PR with a test.