Fix undefined behavior (promoted from a warning to an error in recent gcc)
by casting string objects to const char * before passing to printf.

While here, switch PKG_DESTDIR_SUPPORT from "destdir" to "user-destdir"
(no reason I can see for the former, it appears to date way back) and
add patch comments.

PKGREVISION -> 9, since with netbsd-5 and older -current the issue wasn't
fatal at compile time.

(dholland)