Moved 3 tests to better folders.

--HG--
rename : css21/shand-border-001.xht => css21/borders/shand-border-001.xht
rename : css21/position-absolute-008a.xht => css21/visuren/position-absolute-008a.xht
rename : css21/reference/position-absolute-percentage-inherit-001-ref.xht => css21/visuren/position-absolute-percentage-inherit-001-ref.xht
rename : css21/position-absolute-percentage-inherit-001.xht => css21/visuren/position-absolute-percentage-inherit-001.xht