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/libstd/path.rs

@@ -200,7 +200,7 @@ mod platform {
                         return Some(VerbatimUNC(server, share));
                     } else {
                         // \\?\path
-                        let idx = path.position_elem(&b'\\');
+                        let idx = path.iter().position(|&b| b == b'\\');
                         if idx == Some(2) && path[1] == b':' {
                             let c = path[0];
                             if c.is_ascii() && (c as char).is_alphabetic() {
@@ -214,7 +214,8 @@ mod platform {
                 } else if path.starts_with(b".\\") {
                     // \\.\path
                     path = &path[2..];
-                    let slice = &path[.. path.position_elem(&b'\\').unwrap_or(path.len())];
+                    let pos = path.iter().position(|&b| b == b'\\');
+                    let slice = &path[..pos.unwrap_or(path.len())];
                     return Some(DeviceNS(u8_slice_as_os_str(slice)));
                 }
                 match parse_two_comps(path, is_sep_byte) {