Fixed bug when initialising bitv from bool=true
syntax::ext: replace span_fatal with span_err in many places.

This means that compilation continues for longer, and so we can see more
errors per compile. This is mildly more user-friendly because it stops
users having to run rustc n times to see n macro errors: just run it
once to see all of them.
Fixed typos in comments of librustc backend.
handle zero-size allocations correctly

The `malloc` family of functions may return a null pointer for a
zero-size allocation, which should not be interpreted as an
out-of-memory error.

If the implementation does not return a null pointer, then handling
this will result in memory savings for zero-size types.

This also switches some code to `malloc_raw` in order to maintain a
centralized point for handling out-of-memory in `rt::global_heap`.

Closes #11634
Actually force a / in the path for ext crates

If the library is in the working directory, its path won't have a "/"
which will cause dlopen to search /usr/lib etc. It turns out that Path
auto-normalizes during joins so Path::new(".").join(path) is actually a
no-op.
Make WindowsPath::new("C:foo").root_path() return Some("C:")
Expose platform independent path separators
Disallow implementation of cross-crate priv traits

Turns out we were just forgetting to encode the privacy for trais, and
everything without privacy defaults to public!

Closes #11593
syntax: convert ast_map to use a SmallIntMap.

NodeIds are sequential integers starting at zero, so we can achieve some
memory savings by just storing the items all in a line in a vector.

The occupancy for typical crates seems to be 75-80%, so we're already
more efficient than a HashMap (maximum occupancy 75%), not even counting
the extra book-keeping that HashMap does.
auto merge of #11615 : adwhit/rust/master, r=cmr

This is my first patch so feedback appreciated!

Bug when initialising `bitv:Bitv::new(int,bool)` when `bool=true`. It created a `Bitv` with underlying representation `!0u` rather than the actual desired bit layout ( e.g. `11111111` instead of `00001111`). This works OK because a size attribute is included which keeps access to legal bounds.  However when using `BitvSet::from_bitv(Bitv)`, we then find that `bitvset.contains(i)` can return true when `i` should not in fact be in the set.

```
let bs = BitvSet::from_bitv(Bitv::new(100, true));
assert!(!bs.contains(&127)) //fails
```

The fix is to create the correct representation by treating various cases separately and using a bitshift `(1<<nbits) - 1` to generate correct number of `1`s where necessary.
auto merge of #11616 : huonw/rust/ast_map, r=pnkfelix

NodeIds are sequential integers starting at zero, so we can achieve some
memory savings by just storing the items all in a line in a vector.

The occupancy for typical crates seems to be 75-80%, so we're already
more efficient than a HashMap (maximum occupancy 75%), not even counting
the extra book-keeping that HashMap does.
Squashed commit of the following:

commit d00623d60afd460755b749ad5f94935f756f29d2
Author: musitdev <philippe.delrieu@free.fr>
Date:   Sat Jan 4 22:31:40 2014 +0100

    correct last comments.

commit ef09d6b6d1eebbd7c713c9dad96ed7bfc19dd884
Author: musitdev <philippe.delrieu@free.fr>
Date:   Thu Jan 2 20:28:53 2014 +0100

    update with the last remarks.

commit 46a028fe1fcdc2a7dcdd78a63001793eff614349
Author: musitdev <philippe.delrieu@free.fr>
Date:   Thu Jan 2 10:17:18 2014 +0100

    wrap example code in main function.

commit 2472901929bef09786b7aef8ca7c89fbe67d8e3e
Author: musitdev <philippe.delrieu@free.fr>
Date:   Mon Dec 30 19:32:46 2013 +0100

    Correct code to compile.

commit ed96b2223176781743e984af0e19abcb82150f1f
Author: musitdev <philippe.delrieu@free.fr>
Date:   Thu Dec 5 11:32:28 2013 +0100

    Correct the comment based on the PR comment.
    Change init call to new to reflect last change.

commit 38b0390c3533a16f822a6df5f90b907bd8ed6edc
Author: musitdev <philippe.delrieu@free.fr>
Date:   Wed Dec 4 22:34:25 2013 +0100

    correct from_utf8_owned call.

commit 08bed4c5f4fadf93ec457b605a1a1354323d2f5c
Author: musitdev <philippe.delrieu@free.fr>
Date:   Wed Dec 4 22:12:41 2013 +0100

    correct code '''

commit 02fddcbe2ab37fe842872691105bc4c5cff5abb5
Author: musitdev <philippe.delrieu@free.fr>
Date:   Wed Dec 4 13:25:54 2013 +0100

    correct typing error

commit b26830b8ddb49f551699e791832ed20640a0fafc
Author: musitdev <philippe.delrieu@free.fr>
Date:   Wed Dec 4 13:18:39 2013 +0100

    pass make check

commit e87c4f53286122efd0d2364ea45600d4fa4d5744
Author: musitdev <philippe.delrieu@free.fr>
Date:   Wed Dec 4 10:47:24 2013 +0100

    Add Json example and documentation.
auto merge of #11628 : alexcrichton/rust/issue-11593, r=brson

Turns out we were just forgetting to encode the privacy for trais, and
everything without privacy defaults to public!

Closes #11593
extra::json: add documentation and examples
auto merge of #11633 : chromatic/rust/master, r=alexcrichton
extra::json: add documentation and examples
auto merge of #11635 : thestinger/rust/zero-size-alloc, r=alexcrichton

The `malloc` family of functions may return a null pointer for a
zero-size allocation, which should not be interpreted as an
out-of-memory error.

If the implementation does not return a null pointer, then handling
this will result in memory savings for zero-size types.

This also switches some code to `malloc_raw` in order to maintain a
centralized point for handling out-of-memory in `rt::global_heap`.

Closes #11634
auto merge of #11639 : sfackler/rust/macro-crate-path, r=alexcrichton

If the library is in the working directory, its path won't have a "/"
which will cause dlopen to search /usr/lib etc. It turns out that Path
auto-normalizes during joins so Path::new(".").join(path) is actually a
no-op.
auto merge of #11642 : erickt/rust/path, r=huonw

This pull request exposes a platform independent way to get the path separator. This is useful when building complicated paths by hand.
auto merge of #11643 : kballard/rust/path-root-path, r=erickt