stop using a couple unstable features

It would be nice to build on stable Rust. In particular, I'm hitting
compiler bugs in Rust nightly, such at this one:
rust-lang/rust#38177
I imagine beta/stable compilers would be less problematic.

These two features were easy to get rid of:

* alloc was used to get a Box<[u8]> to uninitialized memory.
  Looks like that's possible with Vec.

* box_syntax wasn't actually used at all. (Maybe a leftover from something.)

The remaining features are:

* plugin, for clippy.
  rust-lang/rust#29597
  I could easily gate it with a "nightly" cargo feature.

* proc_macro, for serde_derive.
  rust-lang/rust#35900
  serde does support stable rust, although it's annoying.
  https://serde.rs/codegen-stable.html
  I might just wait a bit; this feature looks like it's getting close to
  stabilization.

Author: scottlamb

src/main.rs

@@ -29,10 +29,9 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #![cfg_attr(test, feature(test))]
-#![feature(alloc, box_syntax, conservative_impl_trait, plugin, proc_macro)]
+#![feature(conservative_impl_trait, plugin, proc_macro)]
 #![plugin(clippy)]
 
-extern crate alloc;
 extern crate byteorder;
 extern crate core;
 #[macro_use] extern crate chan;

src/mp4.rs

@@ -79,7 +79,6 @@
 extern crate byteorder;
 extern crate time;
 
-use alloc::raw_vec::RawVec;
 use byteorder::{BigEndian, ByteOrder, WriteBytesExt};
 use db;
 use dir;
@@ -366,7 +365,11 @@ impl Mp4Segment {
         let stsz_len = mem::size_of::<u32>() * s.frames as usize;
         let stss_len = mem::size_of::<u32>() * s.key_frames as usize;
         let len = stts_len + stsz_len + stss_len;
-        let mut buf = unsafe { RawVec::with_capacity(len).into_box() };
+        let mut buf = unsafe {
+            let mut v = Vec::with_capacity(len);
+            v.set_len(len);
+            v.into_boxed_slice()
+        };
         {
             let (stts, mut rest) = buf.split_at_mut(stts_len);
             let (stsz, stss) = rest.split_at_mut(stsz_len);