Fix encoding of floating point values into XML.

The encoding functionality in `XMLEncoderAdapter` would throw an exception
when encountering a floating point value, indicating that the value was not
XML serializable.  This has been corrected by adding special handing for
floating point values, analogous to how other data types are handled.

Testing Done:
Added new unit tests to exercise both the JSON and XML encoder adapters.
Encoding is attempted on a variety of data types.  Prior to the fix, the
XML-based test would fail due to the presence of floating point data types.

Reviewed at https://reviews.reviewboard.org/r/8249/

djblets/webapi/encoders.py

@@ -173,6 +173,8 @@ def __encode(self, o, *args, **kwargs):
             self.text(o)
         elif isinstance(o, six.integer_types):
             self.text("%d" % o)
+        elif isinstance(o, float):
+            self.text("%s" % o)
         elif isinstance(o, bool):
             if o:
                 self.text("True")

djblets/webapi/tests/test_encoders.py

@@ -0,0 +1,59 @@
+from __future__ import unicode_literals
+
+import json
+
+from djblets.testing.testcases import TestCase
+from djblets.webapi.encoders import (JSONEncoderAdapter, WebAPIEncoder,
+                                     XMLEncoderAdapter)
+
+
+class EncoderAdapterTests(TestCase):
+    """Tests encoding correctness of WebAPIEncoder adapters"""
+    data = {
+        'dict_val': {'foo': 'bar'},
+        'list_val': [10, 'baz'],
+        'string_val': 'foobar',
+        'int_val': 42,
+        'float_val': 3.14159,
+        'scientific_val': 2.75e-15,
+        'bool_val': True,
+        "none_val": None
+    }
+
+    def test_json_encoder_adapter(self):
+        """Testing JSONEncoderAdapter.encode"""
+        encoder = WebAPIEncoder()
+        adapter = JSONEncoderAdapter(encoder)
+
+        content = adapter.encode(self.data)
+        self.assertEqual(content, json.dumps(self.data))
+
+    def test_xml_encoder_adapter(self):
+        """Testing XMLEncoderAdapter.encode"""
+        encoder = WebAPIEncoder()
+        adapter = XMLEncoderAdapter(encoder)
+
+        expected = (
+            '<?xml version="1.0" encoding="utf-8"?>\n'
+            '<rsp>\n'
+            ' <string_val>foobar</string_val>\n'
+            ' <none_val>\n'
+            ' </none_val>\n'
+            ' <dict_val>\n'
+            '  <foo>bar</foo>\n'
+            ' </dict_val>\n'
+            ' <bool_val>1</bool_val>\n'
+            ' <scientific_val>2.75e-15</scientific_val>\n'
+            ' <int_val>42</int_val>\n'
+            ' <float_val>3.14159</float_val>\n'
+            ' <list_val>\n'
+            '  <array>\n'
+            '   <item>10</item>\n'
+            '   <item>baz</item>\n'
+            '  </array>\n'
+            ' </list_val>\n'
+            '</rsp>'
+        )
+
+        content = adapter.encode(self.data)
+        self.assertEqual(content, expected)