xfail box-related debug-info tests r=snapshot
ignore inherited environment test under valgrind r=snapshot
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.