be accessed now between open()/close(). ownership of the
clipboard is asserted via the empty() method. this parallels
the win32 model (but the win32 code hasn't been updated yet).
refactored X11 clipboard code. moved the bulk of it into
CXWindowsClipboard and moved some comment event handling into
CXWindowsScreen. changed how requests are processed into a
hopefully easier to understand model. added support for getting
clipboard from and sending clipboard to motif (or at least
lesstif) clients. sending to lesstif required a hack to work
around an apparent bug in lesstif.
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