The name rs_entry2modifiable() is more reasonably sized.
For now, leave behind a macro rs_ensure_entry_modifiable in proto-slap.h.

Some noop changes + fixes entry leaks and REP_ENTRY_MODIFIABLE flag leaks.

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. Please note: no real error in the code was found so far, apart from that in syncprov.c and from some config-time error logging; however, errors could slip thru again if things don't change consistently