libstd: remove unnecessary `as_slice()` calls
libsyntax: remove unnecessary `as_slice()` calls
libterm: remove unnecessary `as_slice()` calls
libtest: remove unnecessary `as_slice()` calls
libcollections: remove unnecessary `as_mut_slice()` calls
librustc: remove unnecessary `as_mut_slice` calls
librustc_trans: remove unnecessary `as_mut_slice` calls
librustdoc: remove unnecessary `as_mut_slice` calls
libstd: remove unnecessary `as_mut_slice` calls
libtest: remove unnecessary `as_mut_slice()` calls
libcollections: remove unnecessary `to_string()` calls
libgetopts: remove unnecessary `to_string()` calls
librustc_back: remove unnecessary `to_string()` calls
libserialize: remove unnecessary `to_string()` calls
libstd: remove unnecessary `to_string()` calls
libsyntax: remove unnecessary `to_string()` calls
libterm: remove unnecessary `to_string()` calls
libtest: remove unnecessary `to_string()` calls
libtime: remove unnecessary `to_string()` calls