[SPARK-1610] [SQL] Fix Cast to use exact type value when cast from BooleanType to NumericTy...

...pe.

`Cast` from `BooleanType` to `NumericType` are all using `Int` value.
But it causes `ClassCastException` when the casted value is used by the following evaluation like the code below:

``` scala
scala> import org.apache.spark.sql.catalyst._
import org.apache.spark.sql.catalyst._

scala> import types._
import types._

scala> import expressions._
import expressions._

scala> Add(Cast(Literal(true), ShortType), Literal(1.toShort)).eval()
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Short
	at scala.runtime.BoxesRunTime.unboxToShort(BoxesRunTime.java:102)
	at scala.math.Numeric$ShortIsIntegral$.plus(Numeric.scala:72)
	at org.apache.spark.sql.catalyst.expressions.Add$$anonfun$eval$2.apply(arithmetic.scala:58)
	at org.apache.spark.sql.catalyst.expressions.Add$$anonfun$eval$2.apply(arithmetic.scala:58)
	at org.apache.spark.sql.catalyst.expressions.Expression.n2(Expression.scala:114)
	at org.apache.spark.sql.catalyst.expressions.Add.eval(arithmetic.scala:58)
	at .<init>(<console>:17)
	at .<clinit>(<console>)
	at .<init>(<console>:7)
	at .<clinit>(<console>)
	at $print(<console>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
	at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
	at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
	at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:760)
	at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:805)
	at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:717)
	at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:581)
	at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:588)
	at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:591)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:882)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:837)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:837)
	at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
	at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:837)
	at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:83)
	at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
	at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:105)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
```

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #533 from ueshin/issues/SPARK-1610 and squashes the following commits:

70f36e8 [Takuya UESHIN] Fix Cast to use exact type value when cast from BooleanType to NumericType.
Small changes to release script
SPARK-1488. Squash more language feature warnings in new commits by importing implicitConversion

A recent commit reintroduced some of the same warnings that SPARK-1488 resolved. These are just a few more of the same changes to remove these warnings.

Author: Sean Owen <sowen@cloudera.com>

Closes #528 from srowen/SPARK-1488.2 and squashes the following commits:

62d592c [Sean Owen] More feature warnings in tests
4e2e94b [Sean Owen] Squash more language feature warnings in new commits by importing implicitConversion