Prevent Semantic.gs from overriding top and bottom margins, when it has no business messing with those anyway.
Rewrite %core-clear to be both silent class and mixin, to prevent @media nesting errors when using Semantic.gs  @include row in media queries.
Fixed source order, after foolishly assuming that @mixins got hoisted.
Merge pull request #5 from laustdeleuran/hotfix/semantic-grid-margins

Hotfix: Semantic grid margins and clearfix - sanity check - courtesy of @laustdeleuran