Forbid multiple imports in use statements

Closes #10911
Remove workarounds from issue #4404

Closes #10875
Fix rustdoc output of enums with private variants

Previously, if every variant was private, it would display as a
variantless enum instead of having the "some variants stripped" comment.
s/Second borrow/Previous borrow/ in error messages.

When a borrow occurs twice illegally, Rust will label the other borrow
as the "second borrow".  This is quite confusing, as the "second borrow"
usually happened before the flagged borrow (e.g. as far as dataflow
is concerned, the first borrow is OK, the second borrow is illegal.)
This patch renames "second borrow" to "previous borrow", to make the
spatial relationship between the two borrows clearer.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Don't allow impls to force public types

This code in resolve accidentally forced all types with an impl to become
public. This fixes it by default inheriting the privacy of what was previously
there and then becoming `true` if nothing else exits.

Closes #10545
auto merge of #11019 : alexcrichton/rust/issue-10545, r=pcwalton

This code in resolve accidentally forced all types with an impl to become
public. This fixes it by default inheriting the privacy of what was previously
there and then becoming `true` if nothing else exits.

Closes #10545
auto merge of #11018 : sfackler/rust/variant-strip, r=alexcrichton

Previously, if every variant was private, it would display as a
variantless enum instead of having the "some variants stripped" comment.
auto merge of #11025 : ezyang/rust/reword-second-borrow, r=cmr

When a borrow occurs twice illegally, Rust will label the other borrow
as the "second borrow".  This is quite confusing, as the "second borrow"
usually happened before the flagged barrow (e.g. as far as dataflow
is concerned, the first borrow is OK, the second borrow is illegal.)
This patch renames "second borrow" to "previous borrow", to make the
spatial relationship between the two borrows clearer.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
rustc: Allow `return` to return from a closure.

With the old `for` gone, this behaviour is no longer conflicting with
that use of `return` in closures, and this allows shortcircuiting in a
closure.
auto merge of #10915 : alexcrichton/rust/fixes, r=ILyoan

Just a little cleanup.
auto merge of #11024 : huonw/rust/return-from-closures, r=alexcrichton

With the old `for` gone, this behaviour is no longer conflicting with
that use of `return` in closures, and this allows shortcircuiting in a
closure.
Add a rustdoc test

This is just a smoke test which verifies that the expected files are
generated. Also makes the rmake tests have the right deps.
rustdoc: thread through the context for rendering

This partially reverts 8b5a317.