Add except clauses to LeanMatrix Cython code
trac #17047: Isomorphism of incidence structures
Merge branch 'public/poset_category-17059' of trac.sagemath.org:sage into public/combinat/poset/fix_equality-14019
Current fix by restricting input data to __init__.
Fixed issues with relabeling and elements. Fixed some doctests.
Some more fixes.
reinstated linear_extension
Added function that computes the multipliers of periodic points of affine morhpisms

Also modified documentation for the multiplier function in projective morphism.
getting the interface right!
needed one more relabelling for correct linear extensions
Fixing bugs in relabeling by not doing it automatically in __classcall__.
fixed some docs
Fixed last issues. All doctests pass.
more doc test fixes
Some more documentation as reference.
fixed failing doc tests
fixed more spots where FinitePoset was used directly
fixed doc tests
changes to canonical_label
Fixing doctests.