netcdf preserve file metadata

[Dimitar Misev]

When importing netcdf files the metadata should be preserved precisely, and not converted to string. For example in eobstest

	short tg(time, latitude, longitude) ;
		tg:long_name = "mean temperature" ;
		tg:units = "Celsius" ;
		tg:standard_name = "air_temperature" ;
		tg:_FillValue = -9999s ;
		tg:scale_factor = 0.01f ;

_FillValue and scale_factor should be kept as short and float values, and should not be converted to string.