Unify tests for quadratic field sizes

[fingolfin]

... and some related cleanup

[codecov]

Codecov Report

Merging #42 (03bc2e3) into master (bfbedcd) will not change coverage.
Report is 1 commits behind head on master.
The diff coverage is 70.00%.

@@           Coverage Diff           @@
##           master      #42   +/-   ##
=======================================
  Coverage   47.61%   47.61%           
=======================================
  Files          34       34           
  Lines       17906    17906           
=======================================
  Hits         8526     8526           
  Misses       9380     9380           

Files Changed	Coverage Δ
lib/correlations.gi	45.09% <0.00%> (ø)
lib/gpolygons.gi	24.51% <0.00%> (ø)
lib/projectivespace.gi	55.93% <0.00%> (ø)
lib/enumerators.gi	85.72% <100.00%> (ø)
lib/group.gi	63.34% <100.00%> (ø)
lib/polarspace.gi	61.60% <100.00%> (ø)