- line2d::getLength now returning type T. f64 would actually be fine, but then it has to be used throughout, here the cast to T happens before already, so returning f64 is just confusing as looks like it would return a greater accuracy than it has at that point.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4115 dfc29bdd-3216-0410-991c-e03cc46cb475