bug#17941: `define-method' special-cases zero-subform body

[Taylan Ulrich Bayirli/Kammer]

The `define-method' macro (deferring to the `method' macro) in
modules/oop/goops.scm special-cases a method body of zero forms,
making it (if #f #f).  I don't know if this has a purpose in first
place, but the following fails nevertheless, making the special-case
seem moot and introducing an inconsistency:

(define-method (foo) (begin))

Related bug report:
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17940

Bug originally mentioned in:
http://lists.gnu.org/archive/html/guile-user/2014-07/msg00007.html

Taylan