horiz_interp fixes for r4 tests

[rem1776]

Description
Fixes the r4 tests to build properly (see issue below) and makes some adjustments in the code for when using kind 4 reals. Tolerances needed to be a bit large for the bicubic test in particular, not sure if thats just due to the algorithm.

Fixes #1735

How Has This Been Tested?
make distcheck on amd box

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes