In debuginfo::create_local_var, handle pattern bindings

[catamorphism]

This function just fails if given a local that isn't a pat_ident.

[emberian]

Still a bug, /cc @michaelwoerister

[michaelwoerister]

This will be solved once https://github.com/michaelwoerister/rust/tree/destructuring gets merged into master. It already works very well (all tests in destructured-local.rs and destructured-fn-argument.rs pass).