Fix memleak in bmp.getPixels(True) [fixes #562]

It should be fixed, afaik the reason is that ```pBufCopy``` would not be deallocated automatically as 
"[The caller is responsible for the data ptr](https://docs.python.org/2.7/c-api/buffer.html?highlight=pybuffer_new#c.PyBuffer_FromMemory)" when using ```PyBuffer_FromMemory```, when the PythonObject is destroyed.

[```PyBuffer_New``` maintains its own memory](https://docs.python.org/2.7/c-api/buffer.html?highlight=pybuffer_new#c.PyBuffer_New) so it should automatically deallocate the memory.
(It works for the sample program given in #562 )