in BN_clear_free, don't cleanse the data if the static data flag is set.

in BN_clear_free, don't cleanse the data if the static data flag is set.
much debugging work done by otto. ok miod otto.

side note: BN_FLG_STATIC_DATA doesn't actually mean the data is static.
it's also used to indicate the data may be secretly shared behind your back
as a sort of poor man's refcounting, but without the refcounting.