Gettext configure check needs -liconv on OpenBSD.

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=3921

Reported by Adam Montague, Sirius Hosting amontague@siriushosting.com

At the gettext configure check for -lintl, it fails on openbsd with: /usr/local/lib/libintl.so.2.0: undefined reference to libiconv_open' /usr/local/lib/libintl.so.2.0: undefined reference to libiconv_close' /usr/local/lib/libintl.so.2.0: undefined reference to `libiconv'

Adding -liconv makes it pass this configure test.