Full rewrite of metadata handling. This fixes power failures and crashes

Full rewrite of metadata handling.  This fixes power failures and crashes
that caused illegal checksums.  The new metadata code is more or less ready
to deal with other vendor's metadata formats.

While here clean up the name space.

Fix thib's pool mess by adding removing bad flags in interrupt context.

tested on macppc, amd64, i386, sparc64 & hppa

sparc64 has issues with crypto however those do not seem to be softraid
specific.

help from okan@ ckuethe@ Will Backman and others