[SPARK-4065] Add check for IPython on Windows

This issue employs logic similar to the bash launcher (pyspark) to check
if IPTYHON=1, and if so launch ipython with options in IPYTHON_OPTS.
This fix assumes that ipython is available in the system Path, and can
be invoked with a plain "ipython" command.

Author: Michael Griffiths <msjgriffiths@gmail.com>

Closes #2910 from msjgriffiths/pyspark-windows and squashes the following commits:

ef34678 [Michael Griffiths] Change build message to comply with [SPARK-3775]
361e3d8 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows
9ce72d1 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows

bin/pyspark2.cmd

@@ -59,7 +59,12 @@ for /f %%i in ('echo %1^| findstr /R "\.py"') do (
 )
 
 if [%PYTHON_FILE%] == [] (
-  %PYSPARK_PYTHON%
+  set PYSPARK_SHELL=1
+  if [%IPYTHON%] == [1] (
+	ipython %IPYTHON_OPTS%
+  ) else (
+	%PYSPARK_PYTHON%
+  ) 
 ) else (
   echo.
   echo WARNING: Running python applications through ./bin/pyspark.cmd is deprecated as of Spark 1.0.