Several important additions to the zooming capability:  - A double click now zooms by 2X, centered at the mouse cursor.  If the    cursor is too close to the boundary to allow this, an appropriately    higher magnification is used.  - The zoomed window positions are retained and can be recalled.  The keys    "b" (backward) and "f" (forward) are used to traverse the window list.
Several important additions to the zooming capability:
 - A double click now zooms by 2X, centered at the mouse cursor.  If the
   cursor is too close to the boundary to allow this, an appropriately
   higher magnification is used.
 - The zoomed window positions are retained and can be recalled.  The keys
   "b" (backward) and "f" (forward) are used to traverse the window list.

svn path=/trunk/; revision=1369

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