TS-2174: Fix StatBinaryEval() on div operation

We should fore the type of result to be RecFloat on div operation,
otherwise we can't get the fraction when dividing two RecInt.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>
TS-2005: choke the message until we send the first request.
TS-2174: Assign proper type for uninitialized expression token

In librecords, not all token are register at initialization,
we must assign proper type if it is undefined.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>
TS-1637