Issue #9629 -- permit freezing `&mut` found within an `&` pointer
Address nits for PR for #9629
Make main pub in test case (cc #9629)
Fix test case harder (cc #9629)
auto merge of #10787 : nikomatsakis/rust/issue-9629-freeze-andmut, r=pnkfelix

See #9629 for details.

r? @pnkfelix