Remove trailing whitespace with URL in make_url at once
Fix font-weight propery

Currently, hard coded value(FontWeight300) is used for font-weight property.
To display it properly, use parsed CSS font-weight value.
fix unit of clientrect &
add width,height test in src/test/html/content/test_getBoundingClientRect.html
auto merge of #1452 : deokjinkim/servo/font_weight, r=jdm

Currently, hard coded value(FontWeight300) is used for font-weight property.
To display it properly, use parsed CSS font-weight value.
auto merge of #1451 : ksh8281/servo/fix_unit_of_clientrect, r=jdm

this pr fixes #1076
auto merge of #1446 : sammykim/servo/load_url, r=SimonSapin

1. We must remove trailing whitespace. It makes crash.
Remove needless code.

This `OK(())` should be propagated from `Element.set_attribute()`.
Split up the utility function to make internal attribute's namespace.
Enable only remove operation for Document::update_idmap().
Implement Element.removeAttribute()/removeAttributeNS().