Add plsxwin to python raw API.  This is non-common API, but it was traditionally included in the python plplot API, and, for example, qplplot.py uses it.
Add plsxwin to python raw API.  This is non-common API, but it was
traditionally included in the python plplot API, and, for example,
qplplot.py uses it.

svn path=/trunk/; revision=3878

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot