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.
and literals with the 'f32' or 'f64' suffixes work as well. In
addition, logging things with the f32 or f64 type works. (float is
still assumed to be a synonym for f64).
