rename the Ptr trait to RawPtr

Closes #6607

src/libstd/str.rs

@@ -30,7 +30,7 @@ use libc;
 use option::{None, Option, Some};
 use old_iter::{BaseIter, EqIter};
 use ptr;
-use ptr::Ptr;
+use ptr::RawPtr;
 use str;
 use to_str::ToStr;
 use uint;