Conflicts:
	.travis.yml

This PR reverts https://github.com/rust-lang/rust/pull/17620, which caused a significant regression for slices.

As discussed with @alexcrichton, all of the public-facing changes of the earlier PR need to be rolled back, and it's not clear that we should move the libraries over to this new notation yet anyway (especially given its feature-gated status).

Closes #17710

Instead, only run `make tidy`. The tidy script can run quite quickly, and it's
super annoying to run tests for 50 minutes only to have bors fail with a
"trailing whitespace" error.

Conflicts:
	src/libcollections/lib.rs
	src/libcore/lib.rs
	src/librustdoc/lib.rs
	src/librustrt/lib.rs
	src/libserialize/lib.rs
	src/libstd/lib.rs
	src/test/run-pass/issue-8898.rs

Instead, only run `make tidy`. The tidy script can run quite quickly, and it's
super annoying to run tests for 50 minutes only to have bors fail with a
"trailing whitespace" error.

This test has recently been failing on the bots, and I'm not entirely sure why.
I haven't been able to reproduce locally or on the bots, so I'm adding some
messages to help diagnose the problem hopefully.

Fixes #17169.
Fixes #17649.

The bitshifts were wrong in that they invoked undefined behavior and
only passed the lower byte of the presumed-to-be-32bit errno value.
Apparently all actually possible values for errno happen to be easily
under 256, so this didn't cause any actual problems.

This commit fixes the bitshifts, but doesn't generalize to errno types
that aren't 32bit.

The returned size is the new real size of the allocation.

Fixes #17190

This reverts commit 40b9f5de.

This reverts commit df2f1fa7.

This reverts commit 95cfc356.

This reverts commit 6e0611a4.

Removes an unnecessary allocation when passing the command line arguments to the librustc driver.