Modified the generate_fill algorithm to erase the comment layer from
the flattened cell before painting it in the area to fill;  otherwise,
any existing comment areas would interfere with the fill algorithm.
diff --git a/scripts/generate_fill.py b/scripts/generate_fill.py
index cf09e5e..a292e8b 100755
--- a/scripts/generate_fill.py
+++ b/scripts/generate_fill.py
@@ -166,6 +166,8 @@
         print('        property GDS_FILE ""', file=ofile)
         # Set boundary using comment layer, to the size of the step box
 	# This corresponds to the "topbox" rule in the wafflefill(tiled) style
+        print('        select top cell', file=ofile)
+        print('        erase comment', file=ofile)
         print('        box values $xlo $ylo $xhi $yhi', file=ofile)
         print('        paint comment', file=ofile)
         print('        puts stdout "Writing GDS. . . "', file=ofile)