Presto support
 * add 'presto' engine, but currently 'default' schema is only supported

Squashed commit of the following:

commit b3de4e251b82e703ea72623759e423a169e2a879
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Thu Jan 23 16:57:05 2014 +0900

    add configuration checks

commit 79007e253aa4dcdc0e6526306853a5d70385971e
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Thu Jan 23 13:47:26 2014 +0900

    fix bug of variable definition order

commit 5cbec51427dea900a741e1427332da484dbab7b8
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Thu Jan 23 13:44:46 2014 +0900

    Fix schema name for execute in presto engine temporally
     * presto query execution needs schema(dbname)
       * but current shib UI does not have such UI
     * multi engine + db plan exists just after this branch

commit 3530a20cc4266f925c03d2be557d13c7e276ed7d
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Thu Jan 23 13:33:42 2014 +0900

    fix to send dummy database name for schema listing

commit 0de44ad5a16dcfd4370e759b68bc130b85772ece
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Wed Jan 22 22:22:34 2014 +0900

    add presto engine

commit 835e807f36fc54ebbcfc0142b16e9b1869ffef2c
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Wed Jan 22 22:20:15 2014 +0900

    remove nonsense comment

commit 1d1ee30f687b354325b706ddc0508071b958fbca
Author: TAGOMORI Satoshi <tagomoris@gmail.com>
Date:   Wed Jan 22 21:56:13 2014 +0900

    fix to simplify return value of schema callback