Add a proper channel wrapper to JavaHL, and use it to implement the
tunnel agent callbacks.

* subversion/bindings/javahl/native/jniwrapper/jni_channel.hpp,
  subversion/bindings/javahl/native/jniwrapper/jni_channel.cpp:
   New; channel wrapper implementation.

* subversion/bindings/javahl/native/jniwrapper/jni_env.hpp
  (Java::Env::GetDirectBufferAddress): New JNI function wrapper.
* subversion/bindings/javahl/native/jniwrapper/jni_array.hpp
  (Java::ByteArray::ByteArray): New constructor for uninitialized arrays.
* subversion/bindings/javahl/native/jniwrapper/jni_exception.hpp
  (Java::IOException): New exception generator.
* subversion/bindings/javahl/native/jniwrapper/jni_base.cpp
  (Java::IOException::m_class_name): Initialize.

* subversion/bindings/javahl/native/org_apache_subversion_javahl_util_TunnelChannel.cpp:
   Reimplement everything using the new channel wrapper and jniwrapper.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1540764 13f79535-47bb-0310-9956-ffa450edef68