collections: Split the collections feature

This commit also deprecates the `as_string` and `as_slice` free functions in the
`string` and `vec` modules.

src/libstd/lib.rs

@@ -110,7 +110,9 @@
 #![feature(box_raw)]
 #![feature(box_syntax)]
 #![feature(char_internals)]
+#![feature(clone_from_slice)]
 #![feature(collections)]
+#![feature(collections_bound)]
 #![feature(const_fn)]
 #![feature(core)]
 #![feature(core_float)]
@@ -126,6 +128,8 @@
 #![feature(libc)]
 #![feature(linkage, thread_local, asm)]
 #![feature(macro_reexport)]
+#![feature(slice_concat_ext)]
+#![feature(slice_position_elem)]
 #![feature(no_std)]
 #![feature(num_bits_bytes)]
 #![feature(oom)]
@@ -142,6 +146,7 @@
 #![feature(unicode)]
 #![feature(unique)]
 #![feature(unsafe_no_drop_flag, filling_drop)]
+#![feature(vec_push_all)]
 #![feature(wrapping)]
 #![feature(zero_one)]
 #![cfg_attr(test, feature(float_from_str_radix))]