deps: update to crossbeam-channel 0.3

This also requires corresponding updates to both rand and rand_core. Doing
an update of rand without doing an update of rand_core results in
compilation errors because two distinct versions of rand_core are included
in the build, and the traits they expose are distinct and incompatible.

We also switch over to using tempfile instead of tempdir, which drops the
last remaining thing keeping rand 0.4 in the build.

Fixes #1141, Fixes #1142

ignore/examples/walk.rs

@@ -37,19 +37,19 @@ fn main() {
             Box::new(move |result| {
                 use ignore::WalkState::*;
 
-                tx.send(DirEntry::Y(result.unwrap()));
+                tx.send(DirEntry::Y(result.unwrap())).unwrap();
                 Continue
             })
         });
     } else if simple {
         let walker = WalkDir::new(path);
         for result in walker {
-            tx.send(DirEntry::X(result.unwrap()));
+            tx.send(DirEntry::X(result.unwrap())).unwrap();
         }
     } else {
         let walker = WalkBuilder::new(path).build();
         for result in walker {
-            tx.send(DirEntry::Y(result.unwrap()));
+            tx.send(DirEntry::Y(result.unwrap())).unwrap();
         }
     }
     drop(tx);