Generated Tiff overviews are always uncompressed

[daniel112@…]

Generating overviews for a compressed tiff results in uncompressed overviews.
Changing the compression parameter of TIFF_WriteOverview in GTIFFBuildOverviews
from COMPRESSION_NONE to COMPRESSION_PACKBITS doesn't help, gdaladdo says "In
place update to compressed TIFF images not supported"

[warmerdam]

The within-TIFF overview generator should try and use the compression type of
the base image. 

The exteral overviews in .ovr file code should allow some sort of control of
the compression type, even if it is only via CPLSetConfigOption() for now. 

Andrey, if you have the time and inclination then please feel free to "seize"
this bug, and add me to the cc: list.  

[dron]

Ok, I shall take a look shortly.

[dron]

I have added COMPRESS_OVERVIEW option to control overviews compression methods.
It can be used in the following manner:

gdaladdo --config COMPRESS_OVERVIEW DEFLATE erdas.img 2 4 8 16

Embedded overviews should inherit compression method from the base file, but
libtiff from CVS required to get this feature working. I shall update the
internal GDAL libtiff from the CVS on this week. Almost all files should be
changed, because I have made many changes in the libtiff recently.