Append a new string entry to the property list, possibly
* overwriting an already existing entry with the same key. An
* internal copy of the data passed is made. Will accept only valid
* UTF-8. The string passed in must contain a '='. Left hand side of
* the '=' is used as key name, the right hand side as string
* data. Returns zero on success. \since 0.9.16
Append a new string entry to the property list, possibly * overwriting an already existing entry with the same key. An * internal copy of the data passed is made. Will accept only valid * UTF-8. The string passed in must contain a '='. Left hand side of * the '=' is used as key name, the right hand side as string * data. Returns zero on success. \since 0.9.16