* Fix SRL hang when exit.

* Error occurred when enable Async Load in TestDataProvider.
  * It because DataProvider is calling getNextBatchInternal in one thread, and destructing DataProvider in other thread.
  * Add wait routine in DataProvider destructing.
* Also fix another bug, when destructing TestDataProvider and do not read any test data.

Fix #286

* Follow comments, Use mutex is cool!

* Replace DataProviderWrapperConverter with DataProviderConverter in all
demo prediction scripts.

* Minor refinement of swig_py_paddle.rst to keep consistency with the
English version.

ISSUE=4597359 

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1432 1ad973e4-5ce8-4261-8a94-b56d1f490c56

ISSUE=4586495

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1408 1ad973e4-5ce8-4261-8a94-b56d1f490c56