This patch is my proposal to tweak the current curve_cache runtime to store the paths for every spline instead of just the first.
A spline_index integer is added to all modifiers/constraints/etc that evaluate the path so the user can choose which spline of the curve object to use. If the integer is above the # of splines in the object it uses the last one.
This will allow users to use multiple splines in 1 object instead of having to split them apart.