Document update and update_with_key in SmallIntMap.

Move update above for better docs progression.
Fix #15896

Fix ICE when there's an incorrect enum variant constructor in match arm.

Closes #15896.
rustllvm: Don't require null terminators in files

Apparently the default getFile implementation for a memory buffer in LLVM ends
up requiring a null terminator at the end of the file. This isn't true a good
bit of the time apparently on OSX. There have been a number of failed
nightly/snapshot builds recently with this strange assertion.

This modifies the calls to MemoryBuffer::getFile to explicitly not ask for a
null terminator.
auto merge of #15779 : alexcrichton/rust/no-nul-terminator, r=pcwalton

Apparently the default getFile implementation for a memory buffer in LLVM ends
up requiring a null terminator at the end of the file. This isn't true a good
bit of the time apparently on OSX. There have been a number of failed
nightly/snapshot builds recently with this strange assertion.

This modifies the calls to MemoryBuffer::getFile to explicitly not ask for a
null terminator.
auto merge of #15945 : treeman/rust/doc-smallint-update, r=alexcrichton

Forgot two methods, but @alexcrichton was a bit too quick to accept  #15943, so I made a new PR.
auto merge of #15951 : edwardw/rust/issue-15896, r=alexcrichton

Fix ICE when there's an incorrect enum variant constructor in match arm.

Closes #15896.
librustc: Stop desugaring `for` expressions and translate them directly.

This makes edge cases in which the `Iterator` trait was not in scope
and/or `Option` or its variants were not in scope work properly.

This breaks code that looks like:

    struct MyStruct { ... }

    impl MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

    for x in MyStruct { ... } { ... }

Change ad-hoc `next` methods like the above to implementations of the
`Iterator` trait. For example:

    impl Iterator<int> for MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

Closes #15392.

[breaking-change]
auto merge of #15809 : pcwalton/rust/dedesugar-for, r=pnkfelix

librustc: Stop desugaring `for` expressions and translate them directly.

This makes edge cases in which the `Iterator` trait was not in scope
and/or `Option` or its variants were not in scope work properly.

This breaks code that looks like:

    struct MyStruct { ... }

    impl MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

    for x in MyStruct { ... } { ... }

Change ad-hoc `next` methods like the above to implementations of the
`Iterator` trait. For example:

    impl Iterator<int> for MyStruct {
        fn next(&mut self) -> Option<int> { ... }
    }

Closes #15392.

[breaking-change]
librustc: Check built-in trait bounds on implementations when direct
method calls are involved.

This breaks code like:

    impl<T:Copy> Foo for T { ... }

    fn take_param<T:Foo>(foo: &T) { ... }

    fn main() {
        let x = box 3i; // note no `Copy` bound
        take_param(&x);
    }

Change this code to not contain a type error. For example:

    impl<T:Copy> Foo for T { ... }

    fn take_param<T:Foo>(foo: &T) { ... }

    fn main() {
        let x = 3i; // satisfies `Copy` bound
        take_param(&x);
    }

Closes #15860.

[breaking-change]