added warning if automatic nodata value detection returns unreliable value; bugfix for overwriting user defined attributes of GeoArray

io.raster.GeoArray:
- GeoArray:
    - added quiet mode
    - added attribute _gdalDataset_meta_already_set
    - added print output if nodata value had to be detected automatically
    - set_gdalDataset_meta(): added docstring; method is now only called from __init__

numeric.array:
- revised find_noDataVal()

- added new package similarity