PAM proxy mechanism should work for overviews too

[warmerdam]

When GDAL_PAM_PROXY_DIR is set, it should also be used for creation and preservation of overviews (.rrd or .ovr). This appears not to be the case.

eg.

gdaladdo --config GDAL_PAM_PROXY_DIR /home/warmerda/proxy_db --config USE_RRD YES --config HFA_USE_RRD YES utm.png 2
ERROR 6: The PNG driver does not support update access to existing datasets.

GDAL: GDALOpen(utm.png) succeeds as PNG.
GDAL: GDALDriver::Create(HFA,utm.aux,512,512,1,Byte,0x7ffff3a78590)
ERROR 4: Creation of file utm.aux failed.
Overview building failed.
GDAL: GDALClose(utm.png)
GDAL: GDALDeregister_GTiff() called.

It also does not work for .ovr files.

[warmerdam]

Preliminary work on proxy/overview support has been implemented in trunk (r16706, r16704).

Still in need of further testing, and regression tests.

[warmerdam]

Migrated to 1.6-esri branch as part of r17187.

[gaopeng]

Building overviews on a readonly NITF with JP2 compression doesn't fail and stop. Instead, it keeps computing overview blocks and failing to write blocks. It seems it is building overviews using a JP2KAKBand.

It also generated a large aux.xml in proxy folder.

[warmerdam]

This all seems to be working properly now in trunk and 1.6-esri.