Fix large template compilation problem

* SourceMap is not correctly generated and IOException occurs when a compiled .scala has a string literal longer than 32767 (== java.lang.Short.MAX_VALUE)
* The reason of the problem is handling the value of Short type
  * Since Short is **signed**, Short itself cannot handle unsigned 2 byte integer
  * Short value should be correctly converted to Int value through value & 0xFFFF
    * Cut-off highest 16-bit in Int