don't store subpats bound to underscore

also, tweak fix in place for SI-5158 to appease SI-6941
don't store mutable fields from scala.* as we can assume
these classes are well-behaved and do not mutate their
case class fields
adds support for bytecode diffing to ByteCodeTest
test pattern matcher bytecode
skip test if static type <:< expected *primitive value class*
SI-6686 drop valdef unused in flatMapCond's block
SI-6941 tests