Log Message:
update 0.24.5 to 0.24.6
  http://www.klayout.de/development.html
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  Version 0.24.6
  Release date: 2016-03-22
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-  Bugfix: Early delete of plugin object when returning a new object from
   PluginFactory#create_plugin. The returned object was not held, so in Ruby
   the GC could destroy the object. This could lead to crashes in applications
   employing the Plugin API.

-  Bugfix: It was possible to edit read-only macros. For example, it was
   possible to enter new lines in macros marked as read-only. However, these
   changes were not saved.

-  Bugfix: Shift+Tab not working in macro editor. On some platforms, Shift+Tab
   was not working as expected. This key combinations was supposed to
   left-shift a selected block an undo indents.

-  Bugfix: Wrong scaling of layers when doing XOR's with layouts with
   different database units. This happened when the layouts had different
   layers and "summarize missing layers" was disabled.

-  Bugfix: "Search & Replace" was not working properly if named \ 
layers were
   present. Specifically the shape search was not working due to an
   incorrectly formed query.

-  Bugfix: Sizing produced incorrect results in case of slowly varying polygon
   contours. The effect was a contour with spiky distortions where two "almost
   parallel" edges connected.

-  Bugfix: The diff tool was not reporting differences correctly when layers
   were present in one layout while they were not present in the other. This
   happened specficially when "Summarize missing layers" was disabled.

-  Enhancement: New context mode in marker browser: "Current or Any". \ 
In this
   mode, the markers are displayed in the context of the current cell. If that
   is not possible because the markers are given for cells outside the cell
   tree of the current cell, the fallback is to show the markers in the
   current cell as in "Any" mode.

-  Enhancement: More consistent behaviour of cell and category filters in the
   marker browser. For example, the category filter is now also applied when
   selecting a node for a certain cell in the cell branch and if nested
   categories are present, the category filter is applied smarter - not just
   on each category.
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