In plotLimits(), added tryCatch around range(...,na.rm=T) to avoid
warnings when data is all NA.
Remove some args in apply functions, they can be found in the calling
environment without being an argument.
read.table and type.convert will return a logical if all
data matches the na.string value.  Must convert it to numeric.
Added import of eolts, isfs, lattice, maps to eolsonde NAMESPACE.
added import of gWidgets2