Add missing newline to GET requests embedded in multipart requests

The changes to MultipartContent should have no impact, as I don't expect we are
often sending bodiless parts.

HttpRequestContent previously was would not flush if bodiless, however the
writer isn't buffered so the flush is unnecessary.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=96589029

Author: ejona86

google-http-client/src/main/java/com/google/api/client/http/MultipartContent.java

@@ -91,21 +91,25 @@ public void writeTo(OutputStream out) throws IOException {
           headers.setContentLength(contentLength);
         }
       }
-      // write separator
+      // write multipart-body from RFC 1521 §7.2.1
+      // write encapsulation
+      // write delimiter
       writer.write(TWO_DASHES);
       writer.write(boundary);
       writer.write(NEWLINE);
-      // write headers
+      // write body-part; message from RFC 822 §4.1
+      // write message fields
       HttpHeaders.serializeHeadersForMultipartRequests(headers, null, null, writer);
-      // write content
       if (streamingContent != null) {
         writer.write(NEWLINE);
         writer.flush();
+        // write message text/body
         streamingContent.writeTo(out);
-        writer.write(NEWLINE);
       }
+      // terminate encapsulation
+      writer.write(NEWLINE);
     }
-    // write end separator
+    // write close-delimiter
     writer.write(TWO_DASHES);
     writer.write(boundary);
     writer.write(TWO_DASHES);