return value/use extra::test::black_box in benchmarks
extra: Capture stdout/stderr of tests by default

When tests fail, their stdout and stderr is printed as part of the summary, but
this helps suppress failure messages from #[should_fail] tests and generally
clean up the output of the test runner.
Don't copy &Trait and &mut Trait to temporaries for every call.
Ensure an error is raised on infinite recursion
Add function doc comments for extra::url::*
Removed libextra dependency from libsyntax.
Add test for #8860
Expand ItemDecorator extensions in all contexts

Now that fold_item can return multiple items, this is pretty trivial. It
also recursively expands generated items so ItemDecorators can generate
items that are tagged with ItemDecorators!

Closes #4913
Removed the obsolete ast::CallSugar (previously used by `do`).
Invoke gcc with -nodefaultlibs

This will hopefully bring us closer to #11937. We're still using gcc's idea of
"startup files", but this should prevent us from leaking in dependencies that we
don't quite want (libgcc for example once compiler-rt is what we use).
Add MKFILE_DEPS to compiler-rt target

Currently when you run `make -jN` it's likely that you'll remove compiler-rt and
then it won't get cp'd back into the right place. I believe the reason for this
is that the compiler-rt library target never got updated so make decided it
never needed to copy the files back into place. The files were all there at the
beginning of `make`, but then we may clean out the stage0 versions if we unzip
the snapshot again.
rustdoc: Strip impls of stripped private types

In strip-private, also strip impls of traits for private types. This
fixes the search index so searching for "drop", "eq", etc doesn't throw
an exception.
rustdoc: Strip impls of traits on #[doc(hidden)] types

In the strip-hidden pass, record all types that were stripped, and make
a second pass stripping all impls of traits for these types.
tutorial: stronger wording in build instructions
Test fixes and rebase conflicts from rollups

PRs closed as part of this:

Closes #12212 r=alexcrichton
Closes #12215 r=brson
Closes #12246 r=pcwalton
Closes #12247 r=cmr
Closes #12251 r=brson
Closes #12255 r=alexcrichton
Closes #12257 r=alexcrichton
Closes #12258 r=huonw
Closes #12259 r=huonw
Closes #12263 r=kballard
Closes #12269 r=alexcrichton
Update vim syntax for extern crate
Add CheckedDiv to vim syntax
Update restrictions on rustdoc source rendering

The std macros used to be injected with a filename of "<std-macros>", but macros
are now injected with a filename of "<{} macros>" where `{}` is filled in with
the crate name. This updates rustdoc to understand this new system so it'll
render source more frequently.
Add crate to emacs and kate modefiles
Add crate keyword to gedit language spec