more informative progress messages

--vips-progress now tells you nthreads, tile size and nlines. For
example:

$ vips --vips-progress im_shrink big.v x.v 8 8
vips x.v: 2 threads, 2858 x 1 tiles, groups of 4 scanlines
vips x.v: done in 43s
$

ChangeLog

@@ -23,6 +23,7 @@
 - add im_sines() to operation db
 - move im_spatres() to almostdeprecated
 - done gtk-doc for other
+- --vips-progress tells you about nthreads, tile size, nlines
 
 30/11/10 started 7.24.0
 - bump for new stable

TODO

@@ -1,5 +1,4 @@
 
-
 - use |_O_TEMPORARY to open()'s mode on Windows for tmpfiles to increase the
   chances we actually delete
 

libvips/iofuncs/im_open.c

@@ -455,8 +455,19 @@ typedef struct {
 int
 evalstart_cb( Progress *progress )
 {
+	int tile_width; 
+	int tile_height; 
+	int nlines;
+
 	progress->last_percent = 0;
 
+	vips_get_tile_size( progress->im, &tile_width, &tile_height, &nlines );
+	printf( _( "%s %s: %d threads, %d x %d tiles, groups of %d scanlines" ),
+		g_get_prgname(), progress->im->filename,
+		im_concurrency_get(),
+		tile_width, tile_height, nlines );
+	printf( "\n" );
+
 	return( 0 );
 }