std: Deprecate a number of unstable features

Many of these have long since reached their stage of being obsolete, so this
commit starts the removal process for all of them. The unstable features that
were deprecated are:

* cmp_partial
* fs_time
* hash_default
* int_slice
* iter_min_max
* iter_reset_fuse
* iter_to_vec
* map_in_place
* move_from
* owned_ascii_ext
* page_size
* read_and_zero
* scan_state
* slice_chars
* slice_position_elem
* subslice_offset

src/liballoc/boxed.rs

@@ -86,10 +86,13 @@ use core::raw::{TraitObject};
 #[lang = "exchange_heap"]
 #[unstable(feature = "box_heap",
            reason = "may be renamed; uncertain about custom allocator design")]
+#[allow(deprecated)]
 pub const HEAP: ExchangeHeapSingleton =
     ExchangeHeapSingleton { _force_singleton: () };
 
 /// This the singleton type used solely for `boxed::HEAP`.
+#[unstable(feature = "box_heap",
+           reason = "may be renamed; uncertain about custom allocator design")]
 #[derive(Copy, Clone)]
 pub struct ExchangeHeapSingleton { _force_singleton: () }