calc_ecmwf_p.exe only works if all fields are in the same intermediate file

[mgduda]

When ECMWF model-level data are split among multiple intermediate files (e.g, SFC and 3D files), 3-d RH and GHT fields are not produced in the output PRES files, and calc_ecmwf_p.exe stops with the message:

WARNING: Either TT or SPECHUMD not found. No RH will be computed.

A temporary work-around involves concatenating all intermediate files into one for each time period.