ignore-test cleanup

Most of these are old, but some specific messages for specific tests:

* trait-contravariant-self.rs: failed due to a soundess hole:
  rust-lang@05e3248

* process-detatch: rust-lang@15966c3
  says "this test is being ignored until signals are implemented" That's
  not happening for a long time, and when it is, we'll write tests for
  it.

* deep-vector{,2}.rs: "too big for our poor macro infrastructure", and has
  been ignored over a year.

* borrowck-nested-calls.rs's FIXME rust-lang#6268 was closed in favor of
  rust-lang/rfcs#811

* issue-15167.rs works properly now
* issue-9737.rs works properly now
* match-var-hygiene.rs works properly now

Addresses a chunk of rust-lang#3965

src/test/compile-fail/issue-15167.rs

@@ -9,11 +9,6 @@
 // except according to those terms.
 
 // macro f should not be able to inject a reference to 'n'.
-//
-// Ignored because `for` loops are not hygienic yet; they will require special
-// handling since they introduce a new pattern binding position.
-
-// ignore-test
 
 macro_rules! f { () => (n) }