Revision 1904938

Java binding fixes.

* subversion/bindings/javahl/src/org/apache/subversion/javahl/NativeException.java,
  subversion/bindings/javahl/src/org/tigris/subversion/javahl/NativeException.java
  (getMessage): Use StringBuilder instead of StringBuffer and avoid a 
   NullPointerException if message is null.

* subversion/bindings/javahl/tests/org/apache/subversion/javahl/BasicTests.java,
  (testGetMessage): New function to test getMessage's handling of a null message.

Patch by: Thomas Singer @ Syntevo

https://lists.apache.org/thread/6063p5fh1hqptj8zm3kn5hn9pdgsbb3d