This was a temporary hack with global effect. Eventually there will
be a real solution for controlling stack sizes.

This is a trick to fool microbenchmarks. Closes #1681

Closes #1700

Disable lexical block and function debug info caches to improve compilation time while #1694 is unfixed, and fix stack-exhaustion bug in block parent generation.

Conflicts:
	src/comp/driver/driver.rs
	src/comp/middle/trans/base.rs
	src/comp/syntax/parse/lexer.rs

It wouldn't detect cycles that went through several type vars before.

Closes #1464

This makes it possible to de-initialize values anywhere in
memory, which is needed, for example, for a fast imlementation
of vec::pop.

Closes #742

Closes #1304

Removes a bunch of (eventually) unused arguments. Makes span passing to debuginfo
explicit, instead of relying on the (usually incorrect) spans held in the contexts.

Closes #1439

It's less likely to clash with something than 'neg'.

Issue #1520

rustdocs for f32.rs and f64.rs