Made the PySpark shell version checking compatible with Python 2.6.

Author: rxin

python/pyspark/shell.py

@@ -22,7 +22,7 @@
 """
 
 import sys
-if sys.version_info.major != 2:
+if sys.version_info[0] != 2:
     print("Error: Default Python used is Python%s" % sys.version_info.major)
     print("\tSet env variable PYSPARK_PYTHON to Python2 binary and re-run it.")
     sys.exit(1)