Pop local callback for modify

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.

(ConfigReply) for the error messages.

_db_destroy functions.

Note: this breaks LDAP_COMP_MATCH and SLAP_ZONE_MALLOC. But they
were probably broken already anyway.

list because checking is performed on these, rather than the entry.

slap_mods_free() now takes an extra argument indicating whether to
free the values or not.