Fix some wrong assumptions in JavaHL that led to wrong implementation,
and simplify JNI environment handling.

Amongst other things, the assumption that looking at a Java exception
will remove it from the environment was incorrect.

* build.conf (libsvnjavahl): There are no C files in JavaHL.

* subversion/bindings/javahl/native/JNIThreadData.cpp,
  subversion/bindings/javahl/native/JNIThreadData.h: Removed, unused.
* subversion/bindings/javahl/native/libsvnjavahl.la.c: Removed.
   Implementation moved to JNIUtil.cpp.

* subversion/bindings/javahl/native/SVNClient.cpp,
  subversion/bindings/javahl/native/JNIStackElement.cpp,
  subversion/bindings/javahl/native/JNIStackElement.h:
   Removed all references to JNIThreadData.

* subversion/bindings/javahl/native/JNIUtil.h:
   Removed all references to JNIThreadData.
  (JNIUtil::getFormatBuffer, JNIUtil::formatBufferSize,
   JNIUtil::g_initFormatBuffer, JNIUtil::setEnv,
   JNIUtil::setExceptionThrown): Removed.
  (JNIUtil::isExceptionThrown(), JNIUtil::isJavaExceptionThrown()):
   Changed to simple inline implementations.

* subversion/bindings/javahl/native/JNIUtil.cpp:
   Removed implementaitons that were removed from the class declaration.
   (JNI_OnLoad): Remember the VM pointer.
   (JNIUtil::getEnv): Get an environemnt from the JVM.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1533804 13f79535-47bb-0310-9956-ffa450edef68