Portage/Dependency/Normalize.hs: add normalization pass to remove complementary depend derundancy

A snippet from comment:
  v? ( foo/bar )
  u? ( !v? ( foo/bar ) )
gets translated to
  v? ( foo/bar )
  u? ( foo/bar )

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>