Support revert error message on contract.

[cmditch]

contract Reverter {
    function wassup() {
        require(false, "some message");
    }
}

Calling this function will return

0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000d796f7527726520612066636b7200000000000000000000000000000000000000

One must pattern match 0x08c379a0 on each call response, and decode accordingly.