[SPARK-7886] Add built-in expressions to FunctionRegistry.

This patch switches to using FunctionRegistry for built-in expressions. It is based on #6463, but with some work to simplify it along with unit tests.

TODOs for future pull requests:
- Use static registration so we don't need to register all functions every time we start a new SQLContext
- Switch to using this in HiveContext

Author: Reynold Xin <rxin@databricks.com>
Author: Santiago M. Mola <santi@mola.io>

Closes #6710 from rxin/udf-registry and squashes the following commits:

6930822 [Reynold Xin] Fixed Python test.
b802c9a [Reynold Xin] Made UDF case insensitive.
e60d815 [Reynold Xin] Made UDF case insensitive.
852f9c0 [Reynold Xin] Fixed style violation.
e76a3c1 [Reynold Xin] Fixed parser.
52ddaba [Reynold Xin] Fixed compilation.
ee7854f [Reynold Xin] Improved error reporting.
ff906f2 [Reynold Xin] More robust constructor calling.
77b46f1 [Reynold Xin] Simplified the code.
2a2a149 [Reynold Xin] Merge pull request #6463 from smola/SPARK-7886
8616924 [Santiago M. Mola] [SPARK-7886] Add built-in expressions to FunctionRegistry.

1 files changed, 1 insertions, 1 deletions

diff --git a/python/pyspark/sql/dataframe.py b/python/pyspark/sql/dataframe.py
index e9dd05e2d0..9615e57649 100644
--- a/python/pyspark/sql/dataframe.py
+++ b/python/pyspark/sql/dataframe.py
@@ -746,7 +746,7 @@ class DataFrame(object):
         This is a variant of :func:`select` that accepts SQL expressions.
 
         >>> df.selectExpr("age * 2", "abs(age)").collect()
-        [Row((age * 2)=4, Abs(age)=2), Row((age * 2)=10, Abs(age)=5)]
+        [Row((age * 2)=4, 'abs(age)=2), Row((age * 2)=10, 'abs(age)=5)]
         """
         if len(expr) == 1 and isinstance(expr[0], list):
             expr = expr[0]