Moved 3 border and 2 margin tests into their better
and more appropriate folders along with their
associated reference files.

--HG--
rename : css21/border-width-012.xht => css21/borders/border-width-012.xht
rename : css21/border-width-013.xht => css21/borders/border-width-013.xht
rename : css21/reference/border-width-014-ref.xht => css21/borders/border-width-014-ref.xht
rename : css21/border-width-014.xht => css21/borders/border-width-014.xht
rename : css21/margin-backgrounds-002.xht => css21/margin-padding-clear/margin-backgrounds-002.xht
rename : css21/margin-backgrounds-003.xht => css21/margin-padding-clear/margin-backgrounds-003.xht