add failing unit test for too many OBO ids
error method  in OBO to OWL conversion logs stack  backtrace.

add flag to mute error logging.

mute  errors in unmappableExpressionsTest.
 Count number of unmapped axioms.

add method to OboFormatTestBasics to allow strict conversion flag to be
set, so tests that should not generated unmapped exceptions can be made
to throw.
ignored OBO test; this will require investigation