Fix rxdmath problem with abs

[adamjhn]

Semi-compile abs to fabs in rxdmath.

[codecov-commenter]

Codecov Report

Merging #1545 (17fd28f) into master (114d097) will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1545      +/-   ##
==========================================
+ Coverage   42.90%   42.98%   +0.08%     
==========================================
  Files         550      550              
  Lines      110410   110410              
==========================================
+ Hits        47369    47463      +94     
+ Misses      63041    62947      -94     

Impacted Files	Coverage Δ
share/lib/python/neuron/rxd/rxdmath.py	56.47% <ø> (ø)
src/parallel/bbs.cpp	64.55% <0.00%> (+1.68%)	⬆️
src/parallel/bbssrv2mpi.cpp	56.14% <0.00%> (+3.74%)	⬆️
src/nrnmpi/bbsmpipack.cpp	86.15% <0.00%> (+11.28%)	⬆️
src/parallel/bbsclimpi.cpp	50.58% <0.00%> (+22.09%)	⬆️
src/parallel/bbssrvmpi.cpp	44.57% <0.00%> (+27.71%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 114d097...17fd28f. Read the comment docs.