[Xastir] Warning for topOSM users

[Jerry Dunmire]

Two items to be aware of:
  1) Transparency will work only if GraphicsMagick/ImageMagick is
compiled for 8-bit Quantum.
      The default for the GraphicsMagick code base is 8-bit, but the
package for OS X appears to get built with 16-bit Quantum.
      I have recreated the problem (by rebuilding GraphicsMagick on
Ubuntu), but I have not found a fix or a workaround.

  2) There is a problem with refreshing tiles from topOSM.
      For tiles that are more than 7 days old, I wrote the code to
request that the server send tiles only if the tiles are newer than
the present copy. However, for topOSM this seems result in corrupt
and/or incomplete tiles and very slow downloads due to timeouts. The
only work around I know of at this point is to delete the topOSM
tiles. So far I have not seen any OSM servers that properly honor the
'newer than' request (though topOSM behaves the worst!), so I may drop
that 'feature'.

The reason I am pointing out these problems, rather than just
continuing to work on fixes, is that I will not be able to work on
Xastir for 10 days or so.

73,
...jerry
KA6HLD