Fixes #6824 - Correct scan_number() grammar

Show `int_suffix_size` to appear 0 or 1 times
Show `exponent | . dec_lit` to appear 0 or 1 times, to show why `3f;` is a valid number
auto merge of #6825 : caitp/rust/issue-6824, r=Aatch

Show `int_suffix_size` to appear 0 or 1 times
Show `exponent | . dec_lit` to appear 0 or 1 times, to show why `3f;` is a valid number
auto merge of #6798 : alexcrichton/rust/doc-lints, r=pcwalton

These commits perform a variety of actions:

1. The linting of missing documentation has been consolidated under one `missing_doc` attribute, and many more things are linted about.
2. A test was added for linting missing documentation, which revealed a large number of corner cases in both linting and the `missing_doc` lint pass. Some notable edge cases:
  * When compiling with `--test`, all `missing_doc` warnings are suppressed
  * If any parent of the current item has `#[doc(hidden)]`, then the `missing_doc` warning is suppressed
3. Both the std and extra libraries were modified to `#[deny(missing_doc)]` by default.

I believe that the libraries are getting to the point where they're fairly well documented, and they should definitely stay that way. If developing a particular new module, it's easy enough to add `#[allow(missing_doc)]` at the top, but those should definitely be flags for removal in favor of actual documentation.

I added as much documentation as I could throughout std/extra, although I avoided trying to document things that I knew nothing about. I can't say that this lint pass will vouch for the quality of the documentation of std/extra, but it will certainly make sure that there's at least some describing words.

That being said, I may have a different opinion, so I don't mind amending these commits to turn off the lint by default for std/extra if people think otherwise.
Remove a bunch of unnecessary allocations and copies
auto merge of #6829 : dotdash/rust/allocs, r=sanxiyn
Minor documentation addition.
Minor style fix.
Minor grammar fix.
Attempt to get reuse of common code from multiple clones in different directories.
bump clang version
auto merge of #6831 : Xazax-hun/rust/incoming, r=graydon

Minor doc enhancement for: https://github.com/mozilla/rust/issues/4543
auto merge of #6835 : cmr/rust/clang, r=thestinger

current svn version is 3.4
rustc: change 'use' to 'add' in error message, fix #2994
auto merge of #6836 : pnkfelix/rust/fsk-issue6805-ccache-rewrite-basedir, r=catamorphism

Attempt to get reuse of common object code from multiple clones in different directories.

This is a followup to issue #6805.
auto merge of #6340 : graydon/rust/issue-2994, r=graydon
Remove all usage of the global LLVMContextRef

This allows parallel usage of the rustc library
Have JIT execution take ownership of the LLVMContextRef

Also stop leaking the ExecutionEngine created for jit code by forcibly disposing
of it after the JIT code has finished executing