Getting rid of lots more vector +=. (issue #2719)

src/libcore/dvec.rs

@@ -218,7 +218,7 @@ impl extensions<A:copy> for dvec<A> {
             }
            };
 
-           for ts.each { |t| v += [t]/~ };
+           for ts.each { |t| vec::push(v, t) };
            v
         }
     }

src/libcore/vec.rs

@@ -31,7 +31,7 @@ export rsplit;
 export rsplitn;
 export shift;
 export pop;
-export push;
+export push, push_all;
 export grow;
 export grow_fn;
 export grow_set;