Blocks (or statements involving blocks) that end in a semicolon are no
longer considered the block-expression of their outer block. This used
to be an expression block, but now is a statement block:
{ if foo { ret 1; } else { ret 10; } }
This helps clear up some ambiguities in our grammar.
Closes#868. Unfortunately, this causes certain invalid programs to
fail type-checking instead of failing type-state when a type-state
error message would probably be more intuitive. (Although, by any
reasonable interpretation of the static semantics, it technically
ought to be a type error.)
