Add sdifilt(), similar to difilt() but for shorts. plP_image():    change arguments and other operations from PLINT to short.    detect if device is a slow one.    Add extra information to be saved in the plot buffer.    Inhibit writing again to the plot buffer in plP_esc().
Add sdifilt(), similar to difilt() but for shorts.
plP_image():
   change arguments and other operations from PLINT to short.
   detect if device is a slow one.
   Add extra information to be saved in the plot buffer.
   Inhibit writing again to the plot buffer in plP_esc().

svn path=/trunk/; revision=3579

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