Merge pull request #1 from alexisjacq/master

Fix bug in about due to wrong parenthesis
When no model is specified, use *only* the default model (previously was all models)

This fixes several unit-tests.
Do not memoize reasoning results when they are undecided

So that they are re-evaluated at next call
Add a clear_cache method to sqlite backend to discard memoized result

For now, only called when the 'clear' method is invoked (ie dropping the kownledge base)
Should also probably be invoked when retracting knowledge
{undefined -> undecided}

This is more accurate
Significantly improved implementation of lookup

Cf (new) unit-tests for details. Include a better management of undecided types
and actually checking the labels during the lookup.
Make sure the reasoner can survive a clearing of the knowledge base
Partial naive implementation of 'check'

Only checks if the statements are already asserted or inferred in the knowledge base. Does not
check if 'adding the statements would lead to an inconsistency', which is the real semantic of
check.
Improved the ontologic reasonner

The get_missig_taxonomy_stmts method was not complete, a lot of possible deductions was neglected because 1) dynamic onto classes was not updated inside recursives iterations 2) it didn't return new equivalent classes