auto merge of #15493 : brson/rust/tostr, r=pcwalton

This updates https://github.com/rust-lang/rust/pull/15075.

Rename `ToStr::to_str` to `ToString::to_string`. The naive renaming ends up with two `to_string` functions defined on strings in the prelude (the other defined via `collections::str::StrAllocating`). To remedy this I removed `StrAllocating::to_string`, making all conversions from `&str` to `String` go through `Show`. This has a measurable impact on the speed of this conversion, but the sense I get from others is that it's best to go ahead and unify `to_string` and address performance for all `to_string` conversions in `core::fmt`. `String::from_str(...)` still works as a manual fast-path.

Note that the patch was done with a script, and ended up renaming a number of other `*_to_str` functions, particularly inside of rustc. All the ones I saw looked correct, and I didn't notice any additional API breakage.

Closes #15046.

src/libsyntax/ast.rs

@@ -681,7 +681,7 @@ pub enum IntTy {
 
 impl fmt::Show for IntTy {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", ast_util::int_ty_to_str(*self, None))
+        write!(f, "{}", ast_util::int_ty_to_string(*self, None))
     }
 }
 
@@ -696,7 +696,7 @@ pub enum UintTy {
 
 impl fmt::Show for UintTy {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", ast_util::uint_ty_to_str(*self, None))
+        write!(f, "{}", ast_util::uint_ty_to_string(*self, None))
     }
 }
 
@@ -708,7 +708,7 @@ pub enum FloatTy {
 
 impl fmt::Show for FloatTy {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", ast_util::float_ty_to_str(*self))
+        write!(f, "{}", ast_util::float_ty_to_string(*self))
     }
 }