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A general description is here.
The canvas used when plotting on a jpeg() or bmp() device with a transparent background (most often by copying from a screen device with the default transparent background) is now white and not grey.
o It seems file.access() can be unreliable both ways: that is it can also report that access is barred when it is not. (Seen on network file systems.) So install.packages() to a single library no longer makes use of file.access() but checks directory creation instead: it is still possible that you can create a directory but not be allowed to create a .dll or .chm file, at least under Vista.
If the user chooses to register R during installation, a registry entry HKEY_LOCAL_MACHINE\Software\R-core\R\{version}\InstallPath will be added. Users require administrative privileges to create this key. F: for others, the same key will be put under the HKEY_CURRENT_USER root.