Add ice-equivalent precipitation conversion flag

Input precipitation rate is divided by ice density (0.910) when using the p flag to convert from water-equivalent to ice-equivalent precipitation.
Correct lon/lat bug with newer pyproj versions

It seems like newer pyproj versions (1.9.3 and maybe some older) do not handle well transformations of 2D arrays. As it turns out, 1D arrays instead also results in cleaner code.