Changed the code in the read_F_table function to conform to the "expected...

Changed the code in the read_F_table function to conform to the "expected behavior" description in #1572. Adopted a best-of-both-worlds approach, though, and processed the whole input file all the way through, emitting a message for each problem found, before issuing a final error message to stop processing. Updated doc to clarify requirement for uniform spacing of pressure correction points.