fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.

Also fix up all the fallout elsewhere throughout core. It's really nice being
able to have the prelude.

When trying to import nonexistent items from existing modules, specify that
that is what happened, rather than just reporting "unresolved name".

The default versions (atomic_load and atomic_store) are sequentially consistent.
The atomic_load_acq intrinsic acquires as described in [1].
The atomic_store_rel intrinsic releases as described in [1].

[1]: http://llvm.org/docs/Atomics.html

In #6319, several people mentioned they ran into a "computing
fictitious type" ICE in trans. This turns out to be because some
of my recent changes to typeck::check::_match resulted in type errors
getting reported with ty_err as the expected type, which meant the errors
were suppressed, and typechecking incorrectly succeeded (since the errors
weren't recorded).

Changed the error messages in these cases not to use an expected type at all,
rather, printing out a string describing the type that was expected (which is
what the code originally did). The result is a bit repetitive and the
proliferation of error-reporting functions in typeck::infer is a bit annoying,
but I thought it was important to fix this now; more cleanup can happen later.

Don't pass the binary name to the LLVMRustExecuteJIT closure; doesn't
seem to be needed, anyhow.

This check only works for `match`s, the checks (incorrectly) do not run for patterns in
`let`s.

Recommendation of @kud1ing

as part of an autoslice operation (#6272).

Fixes #6272.

its own type. Use a bitset to represent built-in bounds. There
are several places in the language where only builtin bounds (aka kinds)
will be accepted, e.g. on closures, destructor type parameters perhaps,
and on trait types.

&str can be turned into @~str on demand, using to_owned(), so for
strings, we can create a specialized interner that accepts &str for
intern() and find() but stores and returns @~str.

This allows macros to create tests and benchmarks.