TEST: add pz1 test
TEST: Add pz_spice test.
TEST: remove useless files.
Update test pz1: add .OP
TEST: update test pz_spice: add OP, skip butterworth on Travis.
TEST: add m-2m EKV ladder test.
TEST: add tran1, test all tran methods.
Revert "BUGFIX: do not enable DC guessing if not requested or conf."

This reverts commit e2b0a7a4c3eaf76246fc4d96c80b3b57ddc5f3b2.
TEST: relax requirements for diodecw8