some refactor & fix image size compute
add comment & add ref test
add assign_height in box_
Change `get_attr()` to `get_attr_val_for_layout()`.

The old code was used by both layout and script, but was erroneously
borrowing for the layout case (which causes parallelism
problems). script now uses only `value_ref()` or `get_attribute()`, and
layout now has its own unsafe version that dances around the borrows of
`@mut Attr`.
auto merge of #1533 : metajack/servo/unsafe-get-attr, r=jdm

The old code was used by both layout and script, but was erroneously
borrowing for the layout case (which causes parallelism
problems). script now uses only `value_ref()` or `get_attribute()`, and
layout now has its own unsafe version that dances around the borrows of
`@mut Attr`.
auto merge of #1520 : ksh8281/servo/img_s, r=pcwalton

it makes same result with firefix, chrome in http://www.w3.org/Style/CSS/Test/CSS1/current/sec5523.htm
fix text-decoration property in layout
change position of setting inline_data for "<span>asdf<div>b</div></span>" case
fix line-height property
add RareFlowFlags
RareFlowFlags -> ~RareFlowFlags
auto merge of #1506 : ksh8281/servo/inline_add, r=pcwalton

add inline stuff & color support
it makes same result with firefox in "http://www.w3.org/Style/CSS/Test/CSS1/current/sec543.htm"
makes line-height property can inherit