tuttleHost: add check on clip components

Fix #314
tuttleHost/sam-do: improve exception formatting
ProcessGraph: log clean
OfxhImage: use logging instead of assert

Currently if an exception occured during the process of a node, the HOST
ref count will be wrong so we can't use an assert.
OfxhImage: minor log change
ImageEffectNode: add info to exception
AudioVideo plugin: fix log

This class is used by AVReader AND AVWriter, so don't use avwriter in
the logging.
AudioVideo plugin: Add basic video container extensions (hack)

As some versions of LibAV doesn't declare properly all extensions...
ImageMagick plugin: blacklist some extensions that may crash (hack)
update sconsProject