make gen_thumbnails reentrant, the GUI can call it from different threads
[booh] / lib / booh /
drwxr-xr-x   ..
-rw-r--r-- 11386 GtkAutoTable.rb
-rw-r--r-- 1698 UndoHandler.rb
-rw-r--r-- 16456 booh-lib.rb
-rw-r--r-- 12986 html-merges.rb
-rw-r--r-- 611 pre-setup.rb