faster copyto

Author: mcabbott

base/abstractarray.jl

@@ -904,9 +904,18 @@ end
 
 function copyto!(dest::AbstractArray, dstart::Integer, src)
     i = Int(dstart)
-    for x in src
-        dest[i] = x
-        i += 1
+    if haslength(src)
+        checkbounds(dest, i)
+        checkbounds(dest, i + length(src) - 1)
+        for x in src
+            @inbounds dest[i] = x
+            i += 1
+        end
+    else
+        for x in src
+            dest[i] = x
+            i += 1
+        end
     end
     return dest
 end