auto merge of #5584 : nikomatsakis/rust/issue-4846-carry-bound-lifeti…

…me-names-in-fn-types, r=nikomatsakis

Fix pretty-printer test failure by carrying the bound lifetime names through

the types.  Initially I thought it would be necessary to thread this data
through not only the AST but the types themselves, but then I remembered that
the pretty printer only cares about the AST.  Regardless, I have elected to
leave the changes to the types intact since they will eventually be needed.  I
left a few FIXMEs where it didn't seem worth finishing up since the code wasn't
crucial yet.