- raster/BMP/GIF/PCX/TIF: fix dealing with very large data (use

`size_t` as appropriate)
- BMP: lessen heap memory usage by only `malloc()`ing a row, not
  whole file
- GIF: lessen heap memory usage by paging (also simplifies some
  function returns); use standard colour char map
- raster: add `raster_malloc()` to fail > 1GB (avoids very large
  output files that most systems can't handle; also lessens to
  some degree chances of being victim of OOM killer on Linux)
- GUI: printing scale dialog: set maxima on X-dim and resolution
  to keep scale <= 200

frontend_qt/mainWindow.ui

@@ -2008,7 +2008,7 @@ the barcode in X-dimensions</string>
                 <double>0.100000000000000</double>
                </property>
                <property name="maximum">
-                <double>100.000000000000000</double>
+                <double>200.000000000000000</double>
                </property>
                <property name="singleStep">
                 <double>0.500000000000000</double>