"samdb_msg_add_string" cleanup

[Matthias Dieter Wallnöfer]

s4 developers,

we've three important calls which add strings to LDB messages: 
"ldb_msg_add_string", "ldb_msg_add_steal_string" and "samdb_msg_add_string".
They're not equivalent but I'm asking myself if like other "samdb_msg_*" 
calls we should get rid of the last one. The only difference between the 
first and the last one is the talloc'ed string value. Well, and in most 
cases it's equivalent if it's talloc'ed or not (context allocations, 
string literals as "somevalue"...).
Thoughts?

Cheers,
Matthias