Revert rename of Div to Quot
auto merge of #6147 : bjz/rust/numeric-traits, r=brson

After much discussion on IRC and #4819, we have decided to revert to the old naming of the `/` operator. This does not change its behavior. In making this change, we also have had to rename some of the methods in the `Integer` trait. Here is a list of the methods that have changed:

- `Quot::quot` -> `Div::div`
- `Rem::rem` - stays the same
- `Integer::quot_rem` -> `Integer::div_rem`
- `Integer::div` -> `Integer::div_floor`
- `Integer::modulo` -> `Integer::mod_floor`
- `Integer::div_mod` -> `Integer::div_mod_floor`
core: Remove use of deprecated `drop`
syntax: remove parsing destructors
rustc: remove the rest of drop

Removes:

ast::struct_def::dtor
syntax::ast::ii_dtor
syntax::visit::fk_dtor
syntax::ast_map::node_dtor
syntax:struct_dtor
allow parsing attributes on struct fields
syntax: remove parse::token::{dtor,literally_dtor}
remove some warnings
rustdoc: Remove a now invalid test
pipes: use finally to fix pipes::try_recv
auto merge of #6148 : erickt/rust/remove-drop, r=pcwalton

The drop block has been deprecated for quite some time. This patch series removes support for parsing it and all the related machinery that made drop work.

As a side feature of all this, I also added the ability to annote fields in structs. This allows comments to be properly associated with an individual field. However, I didn't update `rustdoc` to integrate these comment blocks into the documentation it generates.
compiletest: stop ignoring all tests.