check reponse tags in ldapmodify; other functions rely on client library, which might need further work.  Also, remove or silence all deprecated API calls

reduce library link tries.

not yet used

Might need a worse #ifdef mess if any non-glibc memrchr() turns up.

Avoid void* pointer arithmetic.
Convert int c to unsigned char, so c=<negative char value> will match.
Do not decrement pointer below start of array (even when value is not used).