Update to 1.21:

* Version 1.21 (released 2011-04-24) [stable]

** build/gettext: Demand gettext >= 0.18.1 in order to get newer M4 files.
The old M4 files associated with 0.17 caused problems on Solaris,
hopefully now fixed.  Reported by Dagobert Michelsen <dam@opencsw.org>
in <http://thread.gmane.org/gmane.comp.lib.gnulib.bugs/25522>.

** build: Improve MinGW cross-compile makefile, see win32/libidn4win.mk.

** build: Visual Studio files fixed to define LIBIDN_BUILDING.
Tiny patch from Waqas Hussain <waqas20@gmail.com>.

** API and ABI is backwards compatible with the previous version.

(wiz)