Searches a GTree using search_func.
The search_func is called with a pointer to the key of a key/value pair in
the tree, and the passed in user_data. If search_func returns 0 for a
key/value pair, then g_tree_search_func() will return the value of that
pair. If search_func returns -1, searching will proceed among the
key/value pairs that have a smaller key; if search_func returns 1,
searching will proceed among the key/value pairs that have a larger key.
Searches a GTree using search_func. The search_func is called with a pointer to the key of a key/value pair in the tree, and the passed in user_data. If search_func returns 0 for a key/value pair, then g_tree_search_func() will return the value of that pair. If search_func returns -1, searching will proceed among the key/value pairs that have a smaller key; if search_func returns 1, searching will proceed among the key/value pairs that have a larger key.