Potential rounding issues

[klayoutmatthias]

Here is a way to reproduce the issue mentioned in https://www.klayout.de/forum/comments.php?DiscussionID=994&page=1#Comment_4547:

• Create a layout, start with a database unit of 0.001 (the default)
• Create a cell and a sub-cell, please some shapes, place the subcell somewhere
• Change to DBU to 0.00100000000001. This requires two steps: first change to something "very different", like 0.002 and then to 0.00100000000001. Note it's shown as "0.001", but the true value can be checked using this Ruby line: RBA::CellView::active.layout.dbu
• Now change the position of the child instance using the instance properties. Enter a value like "5"

Effect: it will round down to 4.999.

This is partially comprehensible since the DBU is bigger than 0.001. But expectation is that the value would be rounded to 5000 DBU rendering 5.00000000005, not less.