navigation block should cut too long names (SOLUTION INCLUDED)

change the name of an activity to a new one very long and WITHOUT SPACES. Choose, for instance, "very_long_name_missing_spaces" (without quotes, if you like)
Look at the navigation block.
You should see something like attachment01.png
In order to have the name not overflowing the block box (attachment02.png) line 3 of the file the file /HEAD/blocks/navigation/styles.css should be changed from

.block_navigation .block_tree li {margin:3px;list-style: none;padding:0;}

to

.block_navigation .block_tree li {margin:3px;list-style: none;padding:0;overflow:hidden;}