Exposed logging to python.
More python logging work.
Lock python in ILogTarget python subclasses.
Merge branch 'master' into python_logging
updated lz4 to revision 98, dated july 1st, 2013.
the override keyword is supported with gcc (4.7 and later) only when the C++11 mode is enabled.  disabling support for the override keyword on gcc for now.
Merge pull request #252 from est77/python_logging

Expose logging in python bindings
appleseed.cli now has the ability to write each tile to disk as soon as it is rendered (enabled with the --continuous-saving command line option).
in continuous saving mode, don't save the rendered frame after rendering has completed.
refactoring.
updated appleseed.package.py.
removed deprecation notice in comment.