specrectify "function=legendre"

- If there are not enough lines identified by specidentify at the
reddest or bluest wavelengths in some arc image, then the default
specrectify "function=polynomial" value does not do a good job at
rectifying the image (straightening out the sky emission lines) at those
deficient wavelengths (reddest/bluest). Changing "function=legendre"
however gets the job done perfectly.