Update to latest rust.

`std::rand` was moved to it's own crate.
Version of rustc: rustc 0.10-pre (4d64441 2014-03-12 15:07:06 -0700)
Update to latest Rust.

Version of rustc: rustc 0.10-pre (4d64441 2014-03-12 15:07:06 -0700)
Change std::rand to rand in lower_triangular.rs
Merge pull request #5 from cacteye/patch-1

Update to latest rust.