Corrected case of Document#characterSet

Resolves #4251
Use .clone() instead of.as_slice().to_string()
Update content tests for Document#characterSet
auto merge of #4265 : ProgramFOX/servo/issue-4251, r=Ms2ger

Resolves #4251
Use or_init where appropriate.
auto merge of #4263 : Ms2ger/servo/or_init, r=jdm
Fix breakage of `./mach test`

When running commands through Registrar.dispatch, mach does not behave
in the same way it would as if it were running through the command line.
Defaults normally provided through a combination of @CommandArgument and
argparse magic are ignored.

I have some ideas as to how to fix this, but until then, this will allow
`./mach test` to run through test-unit properly.
auto merge of #4269 : mttr/servo/mach_test_fix, r=mbrubeck

When running commands through Registrar.dispatch, mach does not behave
in the same way it would as if it were running through the command line.
Defaults normally provided through a combination of @CommandArgument and
argparse magic are ignored.

I have some ideas as to how to fix this, but until then, this will allow
`./mach test` to run through test-unit properly.
Fix path for CEF build.
Update cargo.lock for CEF and fix left over line from libgreen removal.
auto merge of #4207 : glennw/servo/fix-cef, r=larsbergstrom
Rename gfx/render_task.rs -> gfx/paint_task.rs
Rename RenderTask -> PaintTask.
Rename canvas_render_task -> canvas_paint_task
Rename CanvasRenderTask -> CanvasPaintTask.
Rename RenderContext -> PaintContext
Rename RenderLayer -> PaintLayer
Rename RenderRequest -> PaintRequest
Rename RenderChan -> PaintChan
Rename gfx::paint_task::Msg