Fix failing unit tests.

Bug 2534698
Bug 2534665

Change-Id: If07fc7113b517059bee937d019d464e9c1bc600f
diff --git a/proguard.flags b/proguard.flags
index 7183605..be627db 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -157,3 +157,15 @@
   <init>(...);
   *** get(...);
 }
+
+-keep class org.apache.james.mime4j.field.Field {
+  *** getBody(...);
+}
+
+# The following classes are used only by unit tests.
+# We should move them into tests/ if possible.
+
+-keep class org.apache.james.mime4j.message.Message {
+  *;
+}
+