Rename some files.
* INSTALL.windows: Renamed from README.windows.
* Makefile.am (EXTRA_DIST): Update.
* gettext-runtime/INSTALL.windows: Renamed from gettext-runtime/README.windows.
* gettext-runtime/Makefile.am (EXTRA_DIST): Update.
* gettext-runtime/intl/INSTALL.windows: Renamed from gettext-runtime/intl/README.windows.
* gettext-runtime/intl/Makefile.in (DISTFILES.gettext): Update.
* gettext-runtime/libasprintf/INSTALL.windows: Renamed from gettext-runtime/libasprintf/README.windows.
* gettext-runtime/libasprintf/Makefile.am (EXTRA_DIST): Update.
* gettext-tools/INSTALL.windows: Renamed from gettext-tools/README.windows.
* gettext-tools/Makefile.am (EXTRA_DIST): Update.
