SCHEMA-151. Fix to handle ProtocolVersion.

Over-the-shoulder: Milo
Signed-off-by: Christophe Taton <taton@wibidata.com>
SCHEMA-151. bugfix: Decouple layout ProtocolVersion from system ProtocolVersion.

Over-the-shoulder signoff from Christophe Taton <taton@wibidata.com>.
DDLSHELL-14. COUNTER schema spec should have null schema value.

Over-the-shoulder signoff: Kiyan Ahmadizadeh <kiyan@wibidata.com>
DDLSHELL-13. Client API did not properly throw DDLException.

DDLExceptions were swallowed by the InputProcessor rather than
be thrown back to a third-party client.

Also updates KijiSystem to permit multiple clients without
destroying shared state through the shutdown() method.

Signed-off-by: Christophe Taton <taton@wibidata.com>