win32 fix and FSBV triggering condition fix

Hi, i've sync the repo and read the code. Saw there's a typo in libffi-win32.lisp and i've fixed it. And i've added more filenames for libffi.dll.

There's another commit which modifed STRUCTURE-BY-VALUE-P, the new version is for the 
(defctype xxx (:struct yyy))
(defcfun zzz :int (a xxx))
case. libffi functions should be invoked there too. So i used cffi::follow-typedefs to examine that~

Please see if the changes are proper. And i look forward to seeing a new release in 2013. (Then those using quicklisp will see the changes).

Thanks a lot~