[SPARK-13410][SQL] Support unionAll for DataFrames with UDT columns.

## What changes were proposed in this pull request?

This PR adds equality operators to UDT classes so that they can be correctly tested for dataType equality during union operations.

This was previously causing `"AnalysisException: u"unresolved operator 'Union;""` when trying to unionAll two dataframes with UDT columns as below.

```
from pyspark.sql.tests import PythonOnlyPoint, PythonOnlyUDT
from pyspark.sql import types

schema = types.StructType([types.StructField("point", PythonOnlyUDT(), True)])

a = sqlCtx.createDataFrame([[PythonOnlyPoint(1.0, 2.0)]], schema)
b = sqlCtx.createDataFrame([[PythonOnlyPoint(3.0, 4.0)]], schema)

c = a.unionAll(b)
```

## How was the this patch tested?

Tested using two unit tests in sql/test.py and the DataFrameSuite.

Additional information here : https://issues.apache.org/jira/browse/SPARK-13410

Author: Franklyn D'souza <franklynd@gmail.com>

Closes #11279 from damnMeddlingKid/udt-union-all.