bug#16276: defcustom should require a :type

[Glenn Morris]

Package: emacs
Version: 24.3
Severity: wishlist

I think it should be a compile-time error to specify a defcustom without
a type. Currently there is not even a warning.
If you really can't figure out the type, it won't kill you to write
:type 'sexp (but you can almost always do better).