Replace str::raw::buf_as_slice with c_str_to_static_slice. Close #3843.
Remove 'this could be clearer' FIXME. Looks fine. Close #2618.
Tag a bunch of destructors that need mutable self with FIXME for #4330. Close #4943.
auto merge of #7047 : bblum/rust/bug_triage, r=graydon

r? anybody