Add missing clean-* make targets.

Some more recent Servo crates were not cleaned by `make servo-clean`.
Add tests for the bit_struct! macro.

The macro crate, when built with `--test`,
now depends on itself (a version of itself built without `--test`).
This is a bit unusal, but allows testing a syntax extension.
I did not feel like making a new crate just for this,
and these tests do not belong in any of the other existing crates.
Nuke Node's TLayoutData

LayoutData{Ref} structs replaced its usage for quite some time now.
Correct capitalization of "libXrandr-devel" in Fedora prerequisites list.
Remove obsolete TODO comments
Merge pull request #3155 from brunoabinader/nuke-tlayoutdata

Nuke Node's TLayoutData; r=jdm
Merge pull request #3158 from sstangl/master

Correct capitalization of "libXrandr-devel" in Fedora prerequisites list...
Only write the px value in Show for Au

The integer Au value is mostly internal and does not make much sense.

Printing both values is very verbose and hurts readability of debug logs.
Dump display lists when debug!() is enabled for gfx::display_list
Convert back to physical some layout coordinates.
Set the origin of the root element per its writing mode.

It’s not always (0, 0) anymore.
Reftests can opt into --experimental
Add a reftest for basic block layout in a vertical writing mode.
Merge pull request #3152 from SimonSapin/clean

Add missing clean-* make targets.
Merge pull request #3160 from mbrubeck/old-layout-comments

Remove obsolete TODO comments
Update to png::Image::pixels as an enum.

https://github.com/servo/rust-png/pull/42

This does *not* fix the issue in #3154, but makes it fail!()
instead of (maybe?) reading uninitalized memory.
Merge pull request #3110 from SimonSapin/writing-modes-reftest

Add a basic CSS Writing Modes reftest
Run the same tests for make check on all platforms

This target is no longer run in automation; it's for developer convenience, so
it should really run everything.  Also ensure that `check-all` is a superset
of `check`.
Remove a .orig file left over from conflict resolution.
power