Fixed a GIL related bug.

Wrapped all the low level C++ I/O calls with Py_BEGIN_ALLOW_THREADS
Py_END_ALLOW_THREADS.

The serialize/deserialize code is reading from stream, thus it could be
potentially in I/O block and mess up python threads. This is
particularly significant in pydoop.mapreduce.simulator since there we
are emulating the 'server side' hadoop with a multithreaded python
program. It is a mistery why this did not show up in the standard hadoop
tests.
Minor aesthetic changes in simulator.

Down graded some of the logger.info to logger.debug.
More aesthetic changes in the example programs.
Added simulator to the examples list.