fix to issue #38 failure to solved sampled cartesian points

This PR addresses issue #38 
@shaun-edwards please review
This isn't what I intended.  `frame.frame` is the nominal value, but any frame within the tolerances is valid (the tolerance values `upper/lower` should encompass the nominal).  Debug log messages ([here](https://github.com/ros-industrial-consortium/descartes/blob/hydro-devel/descartes_core/include/descartes_core/cart_trajectory_pt.h#L106-L109) should show this.