Add LIBMTP_Get_Children() to read the list of raw IDs of a folder.

src/libmtp.h.in

Index: src/libmtp.h.in
diff --git a/src/libmtp.h.in b/src/libmtp.h.in
index b49d4490fb1e828cc29d8b5340ca08a2143aa17c..2b2f0bbc403ebc00a2b6aa819b85f31063a7545d 100644
--- a/src/libmtp.h.in
+++ b/src/libmtp.h.in
@@ -875,6 +875,10 @@ LIBMTP_file_t *LIBMTP_Get_Filelisting_With_Callback(LIBMTP_mtpdevice_t *,
 LIBMTP_file_t * LIBMTP_Get_Files_And_Folders(LIBMTP_mtpdevice_t *,
 					     uint32_t const,
 					     uint32_t const);
+int LIBMTP_Get_Children(LIBMTP_mtpdevice_t *,
+                        uint32_t const,
+                        uint32_t const,
+                        uint32_t**);
 LIBMTP_file_t *LIBMTP_Get_Filemetadata(LIBMTP_mtpdevice_t *, uint32_t const);
 int LIBMTP_Get_File_Chunk(LIBMTP_mtpdevice_t*, uint32_t, uint32_t, uint32_t,
                           unsigned char**, uint32_t*);