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

compare and modify. Note that line wrapping is disabled; presumably
existing code expects the compare argument to use only a single line.
The manpage should be updated to note whether standard LDIF with
default line wrapping is expected or not. (Add uses default width already.)