Make search_exists consistent with other _exists APIs

Fixes elastic#230 Thanks ncrocfer for the report!

Author: rciorba

elasticsearch/client/__init__.py

@@ -1244,9 +1244,12 @@ def search_exists(self, index=None, doc_type=None, body=None, params=None):
         :arg q: Query in the Lucene query string syntax
         :arg routing: Specific routing value
         """
-        _, data = self.transport.perform_request('POST', _make_path(index,
-            doc_type, '_search', 'exists'), params=params, body=body)
-        return data
+        try:
+            self.transport.perform_request('POST', _make_path(index,
+                doc_type, '_search', 'exists'), params=params, body=body)
+        except NotFoundError:
+            return False
+        return True
 
     @query_params('allow_no_indices', 'expand_wildcards', 'fields',
         'ignore_unavailable', 'level')

elasticsearch/transport.py

@@ -273,7 +273,7 @@ def perform_request(self, method, url, params=None, body=None):
             body = self.serializer.dumps(body)
 
             # some clients or environments don't support sending GET with body
-            if method == 'GET' and self.send_get_body_as != 'GET':
+            if method in ('HEAD', 'GET') and self.send_get_body_as != 'GET':
                 # send it as post instead
                 if self.send_get_body_as == 'POST':
                     method = 'POST'