Use POLYMAKE_COMMAND variable to locate polymake

[fingolfin]

This is defined by polymaking.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.81%. Comparing base (6c3d924) to head (5685dc5).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #138   +/-   ##
=======================================
  Coverage   44.81%   44.81%           
=======================================
  Files         345      345           
  Lines       64893    64893           
=======================================
  Hits        29085    29085           
  Misses      35808    35808           

Files with missing lines	Coverage Δ
lib/Polymake/aspherical.gi	77.07% <100.00%> (ø)

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[fingolfin]

@grahamknockillaree I still want to complete PR #136, but in the meantime this is a tiny change that will help us on the OSCAR side, so I hope this can be in your next HAP release :-)

[grahamknockillaree]

Should I replace

Exec("polymake ....")

everywhere in HAP by

Exec("POLYMAKE_COMMAND ....")

and assume that the POLYMAKE_COMMAND variable has been defined by Polymake?

[fingolfin]

As far as I can tell there are no other occurrences of Exec("polymake " -- If you see any, please let me know where!

Since other code in hap already relies on the polymaking package working, which in turn requires a working POLYMAKE_COMMAND value, I think this change here is safe enough.

[fingolfin]

Though I guess even better would be to switch it to use the polymaking interface. But that's a bigger change and requires testing etc. again.