auto merge of #5824 : bleibig/rust/debuginfo, r=brson

This adds debugging symbol generation for boxes, bare functions, vectors, and strings, along with a tests for boxes and vectors.

Note that gdb will see them as their actual compiled representation with the refcount, tydesc, etc. fields, so if `b` refers to box, `b->boxed` will refer to its value. Also, since you seem to use the [C struct hack](http://c-faq.com/struct/structhack.html) for dynamic vectors, you won't be able to print out the whole vector at once, only one element at a time by indexing specific elements.

diff --cc src/librustc/middle/trans/base.rs
Simple merge

diff --cc src/librustc/middle/trans/debuginfo.rs
Simple merge