Fix a crash in JavaHL when creating a dated revision from native code.

[in subversion/bindings/javahl]
* native/ExternalItem.cpp (Revision::makeJRevision):
   Pass the revision timestamp to the dated revision constructor.

* tests/org/apache/subversion/javahl/UtilTests.java
  (UtilTests.old_externals, UtilTests.old_externals_propval):
   Add a test case for a dated externals declaration to trigger
   construction of a dated Revision from native code.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1542192 13f79535-47bb-0310-9956-ffa450edef68