Support for Rust (syntax highlighting and search only, no static analysis)

Add support for Rust (syntax highlighting and search only, no static analysis). Requires the first commit 'fix js highlighting' which actually fixes highlighting for everything other than C++. There is a one line change to mime.py so we recognise rust files (.rs). And some changes to buglink to support github issues as well as bugzilla. I've maintained backwards compat with existing config files. For an config file to index Rust, see https://dl.dropboxusercontent.com/u/74741329/rust-dxr/dxr.config