[OctDev] new pchip.m

[<Kai...@t-...>]

Hello,

I have commited a new pchip.m function (main/splines). It uses the 
SLATEC/PCHIP function dpchim.f to calculate the derivatives. I did some 
testing and it should work correctly now. So, if you do 1-d interpolation 
give it a test. Suggestions and bug reports are welcome

Bye Kai