Comparison of real numbers in dart

[hkershaw-brown]

gfortran, building lorenz_96 with a warning on comparing reals
FFLAGS = -Wcompare-reals -O2 -ffree-line-length-none $(INCS)
compare_reals.txt

Fortan test-anything (used in some developer tests) has real comparison tools.
https://github.com/NCAR/DART/blob/main/developer_tests/contrib/fortran-testanything/is_r.inc

[hkershaw-brown]

For example: #887

6e2685a