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support for polygons with holes

Paul Murrell 
Hi

This is for developers of extension packages that provide extra
*graphics devices* for R.

In the *development* version of R, support has been added to the
graphics engine for rendering polygons with holes (e.g., maps with lakes 
with islands ...).

The API change is a new dev_Path() function for graphics devices.

The R_GE_version constant (in GraphicsEngine.h) has been bumped up to 8
as a marker of this change.

This means that, at a minimum, all graphics devices should be updated to 
provide dummy implementations of the new functions to just say that the 
feature is not yet implemented (see for example the PicTeX and XFig
devices in the 'grDevices' package).

A full implementation of dev_Path() should be able to render paths that 
consist of multiple sub-paths which can be filled using either the 
even-odd rule or the non-zero winding rule (see the examples in 
polypath() from 'graphics' or grid.path() from 'grid').

Paul