systemd-python: split out realtime and monotonic into separate functions
systemd-python: split out realtime and monotonic into separate functions

This matches the C API more closely, and also enables the
user to get just partial information, should she desire to
do so.

Functions names in error messages are modified to not include
the class name, because Python uses just the function name
into functions declared as METH_NOARGS, and error messages
were inconsistent.

systemd/python-systemd,systemd/python-systemd,Awesense/python-systemd,Awesense/python-systemd,keszybz/python-systemd,again4you/python-systemd,again4you/python-systemd,Awesense/python-systemd,keszybz/python-systemd