std: silence some test warnings.
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.
debuginfo: Made test cases use correct naming convention for variables.
debuginfo: Added test case for local variable scopes.
debuginfo: Added test case for structs with destructor.
debuginfo: Replaced many instances of @ with &.
debuginfo: Added support for region pointers.
debuginfo: Added test case for region pointers pointing to stack values with basic type.
debuginfo: Added test cases for region pointers into heap boxes for basic types.
debuginfo: Fixed some instances of gdb wrongly printing u8/i8 values as chars.
debuginfo: Added more tests for region pointers (tuples, structs).
debuginfo: Added test case for local variables declared with destructuring.
debuginfo: Added test case for function arguments.
debuginfo: Formatting cleanup.
debuginfo: Some corrections after review.
auto merge of #7414 : gifnksm/rust/max_by, r=catamorphism

`max_by` method returns the element that gives the maximum value from the specfied function.
`max_by`/`min_by` are convenient when you want to get the value which has greatest/smallest scores.

Inspired by [ruby's Enumerable module](http://ruby-doc.org/core-2.0/Enumerable.html).