libsyntax: extend generic deriving code to handle almost all possible traits.

This adds support for static methods, and arguments of most types, traits with
type parameters, methods with type parameters (and lifetimes for both), as well
as making the code more robust to support deriving on types with lifetimes (i.e.
'self).
libsyntax: convert #[deriving(IterBytes)] to generic deriving
libsyntax: add #[deriving(Rand, ToStr)].

The former fills each field of a struct or enum variant with a random
value (and picks a random enum variant). The latter makes the .to_str
method have the same output as fmt!("%?", ..).
testsuite: tests for deriving changes and additions
auto merge of #6267 : huonw/rust/syntax-deriving-generaliseder, r=pcwalton

This "finishes" the generic deriving code (which I started in #5640), in the sense it supports everything that I can think of being useful. (Including lifetimes and type parameters on methods and traits, arguments and return values of (almost) any type, static methods.)

It closes #6149, but met with #6257, so the following doesn't work:
```rust
#[deriving(TotalEq)]
struct Foo<'self>(&'self int);
```
(It only fails for `TotalOrd`, `TotalEq` and `Clone`, since they are the only ones that call a method directly on sub-elements of the type, which means that the auto-deref interferes with the pointer.)

It also makes `Rand` (chooses a random variant, fills the fields with random values, including recursively for recursive types) and `ToStr` (`x.to_str()` is the same as `fmt!("%?", x)`) derivable, as well as converting IterBytes to the generic code (which made the code 2.5x shorter, more robust and added support for tuple structs).

({En,De}codable are trickier, so I'll convert them over later.)