Value of WebAPIException should be number

For code like:
tizen.WebAPIException(tizen.WebAPIException.TYPE_MISMATCH_ERR)

the tizen.WebAPIException.TYPE_MISMATCH_ERR should be number, so that
the WebAPIException can be correctly constructed.
Merge pull request #124 from deqing/fix-tizen-exception

Value of WebAPIException should be number