_Actually_ xfail debuginfo tests
Added overview of the debuginfo module at the beginning of debuginfo.rs.
Fixed compiler warnings about unnecessary string allocations in debuginfo.rs
Reordered debuginfo.rs and commented public fns
debuginfo.rs: Removed some static constants not used anymore.
debuginfo.rs: Explained why a function is called although one could think it should not be.
debuginfo.rs: Removed trailing whitespace.
Extended test cases for struct debug information.
Added test cases for different kinds of padding (simple-struct.rs)
Added test cases for nested structs (struct-in-struct.rs)
Fixed debug information bug regarding struct padding.
debuginfo: Added test cases for tuples.
debuginfo: Added test cases for tuples contained in structs.
debuginfo: Many little formatting improvements.