scripttest-tuttle: add a test for unused nodes
minor change
tuttleHost ThreadEnv: add access to the ImageCache and add isRunning
tuttleHost: minor printing clean
tuttleHost ComputeOptions: nothing
tuttleHost: rename OfxhPluginHandle into OfxhPluginLoadGuard

- bug fix with ref/unref, if we throw inside the constructor of
OfxhPluginLoadGuard
getBestPlugin.py: fix previous changes
tuttleHost Graph: fix computeGlobalHashAtTime

Need setup() and setupAtTime() to be able to compute the hash.
tuttleHost: nothing
tuttleHost ProcessGraph: change abort check rules
tuttleHost ThreadEnv: catch exceptions in the thread top level function
pyTuttle: add threads flags

To be able to use IProgressHandle in Python using ThreadEnv (C++ thread) we need to declare to SWIG that binding functions should use "threadblock".