- Moved ToStr implementation of unsigned integers to uint-template.rs.
- Marked the `str()` function as deprecated.
- Forwarded all conversion functions to `core::num::to_str_common()`
and `core::num::from_str_common()`.
- Fixed most places in the codebase where `to_str()` is being used.
- Added uint-template to_str and from_str overflow tests.
"Dual impls" are impls that are both type implementations and trait
implementations. They can lead to ambiguity and so this patch removes them
from the language.
This also enforces coherence rules. Without this patch, records can implement
traits not defined in the current crate. This patch fixes this, and updates
all of rustc to adhere to the new enforcement. Most of this patch is fixing
rustc to obey the coherence rules, which involves converting a bunch of records
to structs.
