This giant commit changes the syntax of Rust to use "assert" for
"check" expressions that didn't mean anything to the typestate
system, and continue using "check" for checks that are used as
part of typestate checking.
Most of the changes are just replacing "check" with "assert" in test
cases and rustc.
ast.ml - added break and cont statements
item.ml - added break and cont statements
lexer.mll - added break and cont statements
token.ml - added break and cont statements
trans.ml - implemented the break statement for the while-loop case
- replaced hash table accesses with get_stmt_depth where needed
type.ml = added break and cont statements
typestate.ml - implemented the break statement for the while-loop case
- added shorthand filter_live_block_slots
walk.ml - added break and cont statements
while-with-break.rs - code for testing while loops
