Fix dn2id cache for back-hdb rename ops

Fix dec to bin for zero value
silence warnings

first round of s/sprintf/snprintf/; the rationale is: truncate error messages rather than buffer overflow; otherwise, assert that no buffer overflow occurred.  In some cases, error handling could be added.

Fixed gcc 4.3 compile issues

don't allow large search operations that touch more entries churn the
existing cached entries.