Partial fix for issue 436.
fix inaccuracy in homogeneousPart, select only lists without common factor
proper definition of homogeneous, add test
Handle tan/atan of constants in normalize.
test guessing facility
Fix issue 441.
add issue #442
add issues #138, #439, #436, #360, #440, #441
add reference
correct test #301, add expected(), fix some formatting.