Use an enum to set set_timeout_or_interval's is_interval field. Fixes #4059
remove comments now that we have more descriptive names
Update rust-layers to fix empty BufferRequest failures

rust-layers will now avoid sending empty buffer requests which can
cause failures when Servo tries to create empty platform surfaces.

Fixes #4060.
implement Document#createAttribute
Fixes 4037. Enable backtrace on run cmd.
auto merge of #4067 : wenderen/servo/document-create-attribute, r=Manishearth

fixes #4054
auto merge of #4074 : mrobinson/servo/empty-tiles, r=jdm

rust-layers will now avoid sending empty buffer requests which can
cause failures when Servo tries to create empty platform surfaces.

Fixes #4060.
Use atom! in place of Atom::from_slice where necessary
auto merge of #4075 : nwin/servo/fix-4037, r=Ms2ger

Fixes #4037
Break out of loop if can't send data

Fixes #4046
Make sure directories aren't getting tested
auto merge of #4072 : frewsxcv/servo/test-files, r=jdm

Fixes #3910
Adds --release flag to ./mach build-cef

Requested by kmc in IRC.

```
11:36 < kmc> while you're mach-ing about, can you modify build-cef to
accept --release like build does?
```
auto merge of #4077 : mttr/servo/mach_build_cef_release, r=kmcallister

Requested by kmc in IRC.

```
11:36 < kmc> while you're mach-ing about, can you modify build-cef to
accept --release like build does?
```
Update mach to latest changes from mozilla-central

Updates the way mach mixes unrecognized arguments and predefined
arguments (see [mozilla bug
1076649](https://bugzilla.mozilla.org/show_bug.cgi?id=1076649) for
details on this change).
Remove allow_all_args from mach commands
auto merge of #4064 : trevorriles/servo/isintervalenum, r=jdm

Created an `IsInterval` enum to improve readability and remove the need for `true // is_interval`

I'm still fairly new to rust. I briefly looked for a way to implement boolean comparisons of the enum but didn't figure out a way. 

Also I'm not attached to any of the names. Let me know what I can fix :)
auto merge of #4068 : Manishearth/servo/atomify, r=jdm
auto merge of #4070 : kparaju/servo/master-mime-sniffer-failing-4046, r=jdm

Fixes #4046

I tested it by:

    ./mach test-wpt --include=XMLHttpRequest > old.log
    # make code changes
    ./mach test-wpt --include=XMLHttpRequest > new.log
    grep panic old.log # SnifferManager panics
    grep panic new.log # No SnifferManager panics
auto merge of #4080 : mttr/servo/mach_update, r=jdm

Updates the way mach mixes unrecognized arguments and predefined arguments (see [mozilla bug 1076649](https://bugzilla.mozilla.org/show_bug.cgi?id=1076649) for details on this change), and also adds support for argument groupings (see [1077272](https://bugzilla.mozilla.org/show_bug.cgi?id=1077272)).

I was running into some annoyances when trying to implement a change that would allow a `--debug` flag to be used in `./mach run` for running Servo through a debugger (basically, the same behavior described under "How do I run Mozilla under gdb?" [here](https://developer.mozilla.org/en-US/docs/Debugging_Mozilla_with_gdb)). This change should make those annoyances go away, and as far as I can tell, it doesn't have an impact on the way any of the existing commands are used.