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Fix builtin_to_str in the case the builtin is not boolean
Fix feature_selector::operator (inserting inputs isn't correct)

Since the values of the ignored features are initialized there exists
redundant inputs, therefore they have to be accumulated instead of
inserted (cause redundant inputs will have no effect).
Add program option to moses to control perm_ratio

perm_ratio is a way to control how many interactions between variables
are generated during representation building for the boolean domain.
Add support for using exemplar features as initial feature set
Improve logging for representation building

Add some more fine logging and remove the DEBUG_INFO macro