Resolve build warnings; part 5

Remove dependence upon URIs for creating the host auth structure

Change-Id: I92dee36fa329a8976b76bbd4991ed3469c6475f2
diff --git a/proguard.flags b/proguard.flags
index 260fa12..230aeb1 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -103,6 +103,10 @@
   *** setRecipient(com.android.emailcommon.mail.Message$RecipientType, com.android.emailcommon.mail.Address);
 }
 
+-keepclasseswithmembers class com.android.emailcommon.internet.MimeHeader {
+  *** writeToString();
+}
+
 -keepclasseswithmembers class com.android.emailcommon.internet.MimeMessage {
   <init>();
   <init>(java.io.InputStream);