[PATCH] Improved JavaHL pool handling

This patch improves pool handling within the JavaHL bindings. The key
idea is to use C++ operator overloading to allow implicit type
conversion from a Pool object to an apr_pool_t *. This allows usage of
a Pool object wherever an apr_pool_t * would be expected. This change
also adds a more OO-esque method of creating and using subpools.

This passes all the tests, I just want make this doesn't break things in
unknown ways.

-Hyrum

[[[
JavaHL: Add implicit type conversion to the C++ Pool class, allowing
objects of this class to be directly used wherever a apr_pool_t * is
expected.

[ in subversion/bindings/javahl/native/ ]
* Pool.h,
  Pool.cpp:
  (Pool): Add a new constructor, which accepts a parent pool. When Pool
  objects are created this way, they are created as subpools of the
  parent.
  (operator apr_pool_t * ): Implicit type conversion to an apr_pool_t *.
  (clear): New function which wraps svn_pool_clear().
  (pool): Remove this getter function in favor of the implicit
  conversion to apr_pool_t *.
  (m_pool): Rename from this...
  (pool): ...to this.

* SVNAdmin.cpp,
  Pool.cpp,
  CopySources.cpp,
  Outputer.cpp,
  Path.cpp,
  SVNClient.cpp,
  Prompter.cpp,
  Targets.cpp,
  Inputer.cpp:
  Use implicit conversion from Pool to apr_pool_t *.
]]]