Add a "cfg_postorder:" printout to the "test domtree" file tests and use
that to check the computed CFG post-order instead of doing it manually
with Rust code.
* Function names should start with %
* Create FunctionName from string
* Implement displaying of FunctionName as %nnnn with fallback to #xxxx
* Run rustfmt and fix FunctionName::with_string in parser
* Implement FunctionName::new as a generic function
* Binary function names should start with #
* Implement NameRepr for function name
* Fix examples in docs to reflect that function names start with %
* Rebase and fix filecheck tests
This test runs the verifier on each function and matches the resulting
verifier error against the "error:" annotation.
Move the existing verifier test into filetests/verifier/ and use the new
syntex.
