Create zip archives for distribution.

Windows still doesn't support tar.gz out of the box. If we're
bothering with project files we might as well make it easy
to get the source releases.

configure.ac

@@ -19,7 +19,7 @@ AC_CONFIG_MACRO_DIR([m4])
 AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
 
-AM_INIT_AUTOMAKE([1.11 foreign no-define])
+AM_INIT_AUTOMAKE([1.11 foreign no-define dist-zip])
 AM_MAINTAINER_MODE([enable])
 LT_INIT