Omit unused implicit argument if return type is immediate.
Add _RUST_STAGE0 #ifdefs
Added _RUST_STAGEN guard to rust_call_tydesc_glue
testsuite: Add passing test for #4735
testsuite: Add working test for #5550
testsuite: Test cases, one xfailed, one not
testsuite: Update core to std
Implementing suggestions from @nikomatsakis
Fix #6696
testsuite: Add main function to issue-5554 test
auto merge of #6707 : catamorphism/rust/issue-5543, r=catamorphism
auto merge of #6775 : yjh0502/rust/issue_6696, r=catamorphism
auto merge of #6731 : thomaslee/rust/issue-6575, r=pcwalton

Fix for #6575. In the trans phase, rustc emits code for a function parameter that goes completely unused in the event the return type of the function in question happens to be an immediate.

This patch modifies rustc & parts of rustrt to ensure that the vestigial parameter is no longer present in compiled code.
Make missing documentation linting more robust

Add some more cases for warning about missing documentation, and also add a test
to make sure it doesn't die in the future.
Allow doc(hidden) and --test to disable doc linting
Require documentation by default for libstd

Adds documentation for various things that I understand.
Adds #[allow(missing_doc)] for lots of things that I don't understand.
libextra: Require documentation by default