Moved 2 cascade and 2 clear tests into their better,
more appropriate folders along with their
necessary reference files.

--HG--
rename : css21/reference/cascade-009a-ref.xht => css21/cascade/cascade-009a-ref.xht
rename : css21/cascade-009a.xht => css21/cascade/cascade-009a.xht
rename : css21/reference/cascade-009b-ref.xht => css21/cascade/cascade-009b-ref.xht
rename : css21/cascade-009b.xht => css21/cascade/cascade-009b.xht
rename : css21/reference/clear-applies-to-009-ref.xht => css21/visuren/clear-applies-to-009-ref.xht
rename : css21/clear-applies-to-016.xht => css21/visuren/clear-applies-to-016.xht
rename : css21/clear-applies-to-017.xht => css21/visuren/clear-applies-to-017.xht