'Borrow' stack closures rather than copying them (e.g., "|x|f(x)"), in prep for making them noncopyable.

This fixes the strange random crashes in compile-fail tests.

This reverts commit 96cd61ad.

Conflicts:
	src/librustc/driver/driver.rs
	src/libstd/str.rs
	src/libsyntax/ext/quote.rs

This almost removes the StringRef wrapper, since all strings are
Equiv-alent now. Removes a lot of `/* bad */ copy *`'s, and converts
several things to be &'static str (the lint table and the intrinsics
table).

There are many instances of .to_managed(), unfortunately.

The first acts on &str and is not nul-terminated, the last two act on strings
that are always null terminated (&'static str, ~str and @str).

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.

&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.

With luck, this will allow rust to compile itself without --cfg flags again...

Fixes #5656.
Fixes #5541.