Python: fixed None usage as Id in session.exec_()

Check must directly compare PyObject* to Py_None singleton, because other method
(checking object equality to python::api::object()) involves user defined
comparing/equality operators.
This is the case with elliptics.Id which has __cmp__ method, which
cannot accept None as an argument.
Merge pull request #332 from shaitan/monitor

Monitor: Added REST-like api for getting monitor statistics.
Merge pull request #334 from ijon/fix-python-none-as-exec-id

Python: fixed None usage as Id in session.exec_()
Merge pull request #335 from shaitan/monitor

Python: fixed writting out of memory.
trans: randomize route table update: select 5 random groups and read table from one random node from each selected group
monitor: fixed monitor header ifdef decoration