Add RngUtils::sample() method for reservoir sampling from iterators
Remove unused automatic cfg bindings Fixes #7169
Add a bunch of tests for closed issues

Closes #3907
Closes #5493
Closes #4464
Closes #4759
Closes #5666
Closes #5884
Closes #5926
Closes #6318
Closes #6557
Closes #6898
Closes #6919
Closes #7222
Rewrite Saturating in terms of CheckedAdd/CheckedSub
auto merge of #8491 : robertknight/rust/7722-reservoir_sampling, r=graydon

Fixes #7722

I had a couple of queries:
- Should this return an array or an iterator?
- Should this be a method on iterators or on the rng? I implemented it in RngUtils as it seemed to belong with shuffle().
auto merge of #8499 : nickdesaulniers/rust/issue7169, r=graydon

review? @brson 
tests are green
auto merge of #8515 : kballard/rust/saturating-checked, r=thestinger

r? @thestinger
Fix a typo in the ifmt dox
Add even more tests

Closes #8248
Closes #8249
Closes #8398
Closes #8401
auto merge of #8485 : alexcrichton/rust/add-tests, r=catamorphism

Closes #3907
Closes #5493
Closes #4464
Closes #4759
Closes #5666
Closes #5884
Closes #5926
Closes #6318
Closes #6557
Closes #6898
Closes #6919
Closes #7222
Deny warnings in stage1+ libsyntax/librustc/librustdoc/librusti/librust
Deny warnings in tests