Implement -bg 0000ff_0.1 form of command line option to allow control of background alpha value.
Implement -bg 0000ff_0.1 form of command line option to allow control of
background alpha value.

svn path=/trunk/; revision=10189

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