Moving 3 table related tests into their better /tables/
folder; made sure that their associated reference files
were properly linked and also their support image.

--HG--
rename : css21/anonymous-table-box-width-001.xht => css21/tables/anonymous-table-box-width-001.xht
rename : css21/border-spacing-percentage-001.xht => css21/tables/border-spacing-percentage-001.xht
rename : css21/reference/caption-position-001-ref.xht => css21/tables/caption-position-001-ref.xht
rename : css21/caption-position-001.xht => css21/tables/caption-position-001.xht