Fix crash on executing URL with hashtag(local bookmark)
Refactor self.recomposite value update
Refactor FontStyle and really fix #193

* Using .connect(", ") just to use .split(",") later is silly.
Keep it a vector.
* The 'font-style' property can not be both italic and oblique.
Use an enum instead of two booleans.
Remove some trailing whitespace
implemented iterator for child elements
auto merge of #1447 : june0cho/servo/fix_crash_on_local_bookmark, r=kmcallister

Local bookmark which is implemented in #1262 is not currently working when executing URL with hashtag(e.g. `test_local_bookmark.html#h3`, `acid2.html#top`).
Local bookmark has two matching processes(http://www.w3.org/TR/html5/browsers.html#scroll-to-fragid). Among two, this commit fixes the crash on ID attribute, and still has crash on `a` element with `name` attribute.
As a result, with this commit, `test_local_bookmark.html#h3` works well, but `acid2.html#top` still does not work.
auto merge of #1455 : SimonSapin/servo/font-style, r=kmcallister

* Using .connect(", ") just to use .split(",") later is silly. Keep it a vector.
* The 'font-style' property can not be both italic and oblique. Use an enum instead of two booleans.
auto merge of #1443 : khodzha/servo/child_elements, r=jdm

implemented child_elements to filter children with is_element predicate
Correctly guard an import in servo.rc.
Avoid mixing up local name and name when creating attributes.
auto merge of #1458 : Ms2ger/servo/unused-import, r=jdm
auto merge of #1459 : Ms2ger/servo/attr-new, r=jdm
Make Element::set_attribute not lower-case the name argument.

In particular, for SetAttributeNS, we should not change the case.
auto merge of #1460 : Ms2ger/servo/set_attribute-no-lowercase, r=jdm

In particular, for SetAttributeNS, we should not change the case.
fix for anonymous block boxes
remove block exception
remove unused import
add comment
fix comment
auto merge of #1461 : ksh8281/servo/block_black_boxes, r=SimonSapin

fix for anonymous boxes.
http://www.w3.org/TR/CSS2/visuren.html#anonymous-block-level