SplineTest: fix gcc5 build. Still 'tuple constructor is explicit' issues :/
SplineTest: fix gcc5 build. Still 'tuple constructor is explicit' issues :/

LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed