Use machine_name element that's now in core for module_name

Upping this to a bug, as the implementation in Features is broken:

1. Start typing a module name
2. Click to edit the machine name yourself
3. Enter your own machine name
4. Go back and change the module name
5. The JS clobbers what you typed in the machine name with the updated human name text.

This is not the same behaviour as core's element.

Here's a patch.

(This also takes care of #1331886: don't disable machine name in rebuild form -- it prevents renaming of features BTW.)

Let's see if we can get this re-rolled and tested for the 2.x branch.

Reroll

Looks good to me, though as it was originally my patch I don't think I can RTBC...

Patch looks good and it works fine for me. Used this to fix a weird bug with the machine-name field always being submitted empty (although it had a valid value).