Case blocks in switch statements now must end in a break, return, or
fallthrough statement to give best mix of safety, readability, and
flexibility.
The new fallthrough keyword explicitly allows control to be passed to the
next case block in a switch statement.
Addresses #754.
Case bodies now don't require a "break" statement to prevent fallthrough
to case bodies below. Empty case bodies generate an error message at
parse-time to help indicate the absence of automatic fallthrough; to
associate multiple values with a case, use "case 1, 2:" instead of
"case 1: case 2:".
They behave like C-style switches except case labels can be comprised
of multiple literal constants delimited by commas. Only atomic types
are allowed for now. Case label bodies that don't execute a "return"
or "break" statement will fall through to subsequent cases. A default
case label is allowed.
