Introduce a set_uint_attribute method.
Remove some more xray code.
Implement Document.createElementNS.
Remove trailing whitespace.
auto merge of #2055 : Ms2ger/servo/trws, r=jdm

Done with `git ls-tree --name-only -r HEAD . | grep "\.rs" | xargs sed -i 's/\s\+$//g'`
Handle an exception from cx.evaluate_script more gracefully.
auto merge of #2057 : Ms2ger/servo/evaluate_script, r=jdm
auto merge of #2053 : Ms2ger/servo/createElementNS, r=jdm

#1391 rebased
auto merge of #2048 : Ms2ger/servo/set_uint_attribute, r=jdm
auto merge of #2051 : Ms2ger/servo/more-xray, r=jdm

On top of #2050
HTMLImageElement attribute getters and setters
Use set_uint_attribute where necessary