Log Message:
Include converters/libiconv/buildlink3.mk in Makefile.common
and bump PKGREVISIONS for lyx-qt and lyx-xforms packages.

lyx uses iconv. The build suggests using libiconv.
Under NetBSD 1.6.2, the lyx-qt build broke when not including
this buildlink. Under Linux and NetBSD 2.x, it built fine before
because it found native iconv() and used it.

Thank you to John R. Shannon for research.

Okayed by maintainer, Martti Kuparinen.