Add interp1q

[John W. Eaton]

On 14-May-2008, David Bateman wrote:

| The benefits of the interp1q function are limited since with faster
| machines than when this function was written for matlab, the portion of
| time used to executed the error checking codein the interp1 function  is
| typically very small. However, for completeness we should probably have
| this function. Changeset attached that makes the same assumptions as the
| matlab interp1q on the input parameters and just copies the relevant
| code from interp1.m

I applied this changeset.

Thanks,

jwe