Ancestral nodes from a founding generation can now be retained in simplify

[gtsambos]

Closes #775 (I think?)

[codecov]

Codecov Report

Merging #781 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #781   +/-   ##
=======================================
  Coverage   87.72%   87.72%           
=======================================
  Files          24       24           
  Lines       19394    19394           
  Branches     3640     3640           
=======================================
  Hits        17013    17013           
  Misses       1290     1290           
  Partials     1091     1091           

Flag	Coverage Δ
#c_tests	85.33% <ø> (ø)
#python_c_tests	90.16% <ø> (ø)
#python_tests	99.02% <ø> (ø)

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[gtsambos]

This can be closed now that #775 has been resolved by #782.