solved symbol size trunc bug thanks to tbonfort

symbol values with fractional size were truncated

here a test sld: https://gist.github.com/luipir/5964556
where ```<se:Size>0.7</se:Size>``` were truncated in: SIZE 0

as suggested by: EvenR changed ```nSize``` in ```dSize``` "to indicate the change of type"

solution has been found in #mapserver chat