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Keen: fix another misuse of dsf_canonify.

Chris Boyle points out that outline_block_structure has a comment
saying that we're supposed to have picked a square with a boundary to
its left. dsf_canonify no longer guarantees that, but dsf_minimal
does. Switch to using that throughout the function.

'keen --generate 10#12345 --print 5x2' failed an assertion before this
fix, and now doesn't.

--- a/keen.c

+++ b/keen.c

@@ -2257,7 +2257,7 @@

      * Iterate over all the blocks.

      */

     for (i = 0; i < a; i++) {

-	if (dsf_canonify(dsf, i) != i)

+	if (dsf_minimal(dsf, i) != i)

 	    continue;

 	/*

@@ -2296,11 +2296,11 @@

 	    tx = x - dy + dx;

 	    ty = y + dx + dy;

 	    nin += (tx >= 0 && tx < w && ty >= 0 && ty < w &&

-		    dsf_canonify(dsf, ty*w+tx) == i);

+		    dsf_minimal(dsf, ty*w+tx) == i);

 	    tx = x - dy;

 	    ty = y + dx;

 	    nin += (tx >= 0 && tx < w && ty >= 0 && ty < w &&

-		    dsf_canonify(dsf, ty*w+tx) == i);

+		    dsf_minimal(dsf, ty*w+tx) == i);

 	    if (nin == 0) {

 		/*

 		 * Turn right.

@@ -2337,9 +2337,9 @@

 	     * somewhere sensible.

 	     */

 	    assert(x >= 0 && x < w && y >= 0 && y < w &&

-		   dsf_canonify(dsf, y*w+x) == i);

+		   dsf_minimal(dsf, y*w+x) == i);

 	    assert(x+dx < 0 || x+dx >= w || y+dy < 0 || y+dy >= w ||

-		   dsf_canonify(dsf, (y+dy)*w+(x+dx)) != i);

+		   dsf_minimal(dsf, (y+dy)*w+(x+dx)) != i);

 	    /*

 	     * Record the point we just went past at one end of the

-- 

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