[SPARK-2097][SQL] UDF Support

This patch adds the ability to register lambda functions written in Python, Java or Scala as UDFs for use in SQL or HiveQL.

Scala:
```scala
registerFunction("strLenScala", (_: String).length)
sql("SELECT strLenScala('test')")
```
Python:
```python
sqlCtx.registerFunction("strLenPython", lambda x: len(x), IntegerType())
sqlCtx.sql("SELECT strLenPython('test')")
```
Java:
```java
sqlContext.registerFunction("stringLengthJava", new UDF1<String, Integer>() {
  Override
  public Integer call(String str) throws Exception {
    return str.length();
  }
}, DataType.IntegerType);

sqlContext.sql("SELECT stringLengthJava('test')");
```

Author: Michael Armbrust <michael@databricks.com>

Closes #1063 from marmbrus/udfs and squashes the following commits:

9eda0fe [Michael Armbrust] newline
747c05e [Michael Armbrust] Add some scala UDF tests.
d92727d [Michael Armbrust] Merge remote-tracking branch 'apache/master' into udfs
005d684 [Michael Armbrust] Fix naming and formatting.
d14dac8 [Michael Armbrust] Fix last line of autogened java files.
8135c48 [Michael Armbrust] Move UDF unit tests to pyspark.
40b0ffd [Michael Armbrust] Merge remote-tracking branch 'apache/master' into udfs
6a36890 [Michael Armbrust] Switch logging so that SQLContext can be serializable.
7a83101 [Michael Armbrust] Drop toString
795fd15 [Michael Armbrust] Try to avoid capturing SQLContext.
e54fb45 [Michael Armbrust] Docs and tests.
437cbe3 [Michael Armbrust] Update use of dataTypes, fix some python tests, address review comments.
01517d6 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into udfs
8e6c932 [Michael Armbrust] WIP
3f96a52 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into udfs
6237c8d [Michael Armbrust] WIP
2766f0b [Michael Armbrust] Move udfs support to SQL from hive. Add support for Java UDFs.
0f7d50c [Michael Armbrust] Draft of native Spark SQL UDFs for Scala and Python.
[SPARK-2785][SQL] Remove assertions that throw when users try unsupported Hive commands.

Author: Michael Armbrust <michael@databricks.com>

Closes #1742 from marmbrus/asserts and squashes the following commits:

5182d54 [Michael Armbrust] Remove assertions that throw when users try unsupported Hive commands.
[SPARK-2729][SQL] Added test case for SPARK-2729

This is a follow up of #1636.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1738 from liancheng/test-for-spark-2729 and squashes the following commits:

b13692a [Cheng Lian] Added test case for SPARK-2729
[SPARK-2797] [SQL] SchemaRDDs don't support unpersist()

The cause is explained in https://issues.apache.org/jira/browse/SPARK-2797.

Author: Yin Huai <huai@cse.ohio-state.edu>

Closes #1745 from yhuai/SPARK-2797 and squashes the following commits:

7b1627d [Yin Huai] The unpersist method of the Scala RDD cannot be called without the input parameter (blocking) from PySpark.
[SPARK-2739][SQL] Rename registerAsTable to registerTempTable

There have been user complaints that the difference between `registerAsTable` and `saveAsTable` is too subtle.  This PR addresses this by renaming `registerAsTable` to `registerTempTable`, which more clearly reflects what is happening.  `registerAsTable` remains, but will cause a deprecation warning.

Author: Michael Armbrust <michael@databricks.com>

Closes #1743 from marmbrus/registerTempTable and squashes the following commits:

d031348 [Michael Armbrust] Merge remote-tracking branch 'apache/master' into registerTempTable
4dff086 [Michael Armbrust] Fix .java files too
89a2f12 [Michael Armbrust] Merge remote-tracking branch 'apache/master' into registerTempTable
0b7b71e [Michael Armbrust] Rename registerAsTable to registerTempTable
SPARK-2602 [BUILD] Tests steal focus under Java 6

As per https://issues.apache.org/jira/browse/SPARK-2602 , this may be resolved for Java 6 with the java.awt.headless system property, which never hurt anyone running a command line app. I tested it and seemed to get rid of focus stealing.

Author: Sean Owen <srowen@gmail.com>

Closes #1747 from srowen/SPARK-2602 and squashes the following commits:

b141018 [Sean Owen] Set java.awt.headless during tests
SPARK-2414 [BUILD] Add LICENSE entry for jquery

The JIRA concerned removing jquery, and this does not remove jquery. While it is distributed by Spark it should have an accompanying line in LICENSE, very technically, as per http://www.apache.org/dev/licensing-howto.html

Author: Sean Owen <srowen@gmail.com>

Closes #1748 from srowen/SPARK-2414 and squashes the following commits:

2fdb03c [Sean Owen] Add LICENSE entry for jquery
[Minor] Fixes on top of #1679

Minor fixes on top of #1679.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1736 from andrewor14/amend-#1679 and squashes the following commits:

3b46f5e [Andrew Or] Minor fixes