{Eventually, this will be expanded to work with any
oce object. But, for now, it only works for vectors that can
be coerced to numeric.}
{If the first or last point is NA, then x
is returned unaltered.}
{Only method linear works now, and that argument is
ignored at present.}
Details
Sequences of NA values, are filled by linear
interpolation between the non-NA values that bound the gap.