Requesting the correct image format direcly makes the request faster,
as PNG is much smaller. This also removes the external dependency on
the Pillow library.

Added logging file, 'OscScreenGrabLAN.py.log'.

Changes from telnet.py of Python 2.7.12 are now merged in telnet_receive_all.py

On a clean Python 2.7.12, 'pillow' must be installed manually.

IMPORTANT !
If you previously had 'PIL' installed, then 'PIL' must be uninstalled.
Install 'pillow' only after uninstalling 'PIL'.

 This is just a draft of the idea - code optimisation strongly needed.

Python 2.7.3 and PIL were already included in Debian