Protocol, interface method declarations don't allow for varags. Currently, for example

  (defprotocol FooBar
    (foo [this & more]))

compiles just fine, and & is interpreted as a usual argument that happens to be
named & without special meaning. But clearly, the user wanted to specify a
varags parameter here. The same applies to definterface.

Similarly, providing method implementations via defrecord, deftype, and reify
don't allow for varags (but dynamic extensions via extend do).

So this patch makes defprotocol and definterface throw an
IllegalArgumentException if a user tries to use varargs in method signatures.

Similarly, defrecord, deftype, and reify throw an IllegalArgumentException if
any method implementation arglist contains a varargs argument.

This patch is a cut-down variant of my patch to http://dev.clojure.org/jira/browse/CLJ-1024
which has been reverted shortly before Clojure 1.5 was released. The CLJ-1024 patch
was the same as this one, but it has also forbidden destructuring in defprotocol and
definterface. This was a bit too much, because although destructuring has no
semantic meaning with method declarations, it still can serve a documentation purpose.

This has been discussed on the list: https://groups.google.com/d/topic/clojure-dev/qjkW-cv8nog/discussion