auto merge of #7123 : huonw/rust/more-str, r=thestinger

Moves all the remaining functions that could reasonably be methods to be methods, except for some FFI ones (which I believe @erickt is working on, possibly) and `each_split_within`, since I'm not really sure the details of it (I believe @kimundi wrote the current implementation, so maybe he could convert it to an external iterator method on `StrSlice`, e.g. `word_wrap_iter(&self) -> WordWrapIterator<'self>`, where `WordWrapIterator` impls `Iterator<&'self str>`. It probably won't be too hard, since it's already a state machine.)

This also cleans up the comparison impls for the string types, except I'm not sure how the lang items `eq_str` and `eq_str_uniq` need to be handled, so they (`eq_slice` and `eq`) remain stand-alone functions.

src/libstd/os.rs

@@ -144,7 +144,7 @@ pub mod win32 {
     }
 
     pub fn as_utf16_p<T>(s: &str, f: &fn(*u16) -> T) -> T {
-        let mut t = str::to_utf16(s);
+        let mut t = s.to_utf16();
         // Null terminate before passing on.
         t += [0u16];
         vec::as_imm_buf(t, |buf, _len| f(buf))