Add virtual assignment operator and copy constructor to SDAI_Select

Related to commit f43a106ac31d (removal of pure virtual assignment operator) -
that commit eliminated an MSVC linker error, but caused a regression on linux
generated code: in select assignment operator, call base class assignment operator
test SDAI_Select assignment operator
improve formatting of generated select class code
cleanup in selects.c
Merge pull request #285 from stepcode/review/ap203min_regression

ap203min regression