add .szi as a synonym for .zip

in dzsave

ChangeLog

@@ -3,6 +3,7 @@
 - better pbm (one bit) load, better pfm (float) load/save
 - added pbm (one bit) save
 - changed vips_gaussblur() parameters, sorry
+- add .szi as a dzsave zip synonym
 
 25/7/14 started 7.41.0
 - start working on --disable-deprecated

libvips/foreign/dzsave.c

@@ -1700,11 +1700,13 @@ vips_foreign_save_dz_build( VipsObject *object )
 	if( (p = strrchr( dz->basename, '.' )) ) {
 		*p = '\0';
 
-		/* If we're writing to thing.zip, default to zip container.
+		/* If we're writing to thing.zip or thing.szi, default to zip 
+		 * container.
 		 */
-		if( strcasecmp( p + 1, "zip" ) == 0 &&
-			!vips_object_argument_isset( object, "container" ) )
-			dz->container = VIPS_FOREIGN_DZ_CONTAINER_ZIP;
+		if( !vips_object_argument_isset( object, "container" ) )
+			if( strcasecmp( p + 1, "zip" ) == 0 ||
+				strcasecmp( p + 1, "szi" ) == 0 )
+				dz->container = VIPS_FOREIGN_DZ_CONTAINER_ZIP;
 	}
 }