Add a new function to API to enable debug mode

To avoid build and build only to enable (or disable) debug mode, we
work now as the lib libusb :)

As libusb, you can do :
  LIBMTP_Set_Debug(flags);
or use an environnement variable :
  export LIBMTP_DEBUG=flags

flags value details :
   *  0x00 [0000 0000] : no debug (default)
   *  0x01 [0000 0001] : PTP debug
   *  0x02 [0000 0010] : Playlist debug
   *  0x04 [0000 0100] : USB debug
   *  0x08 [0000 1000] : USB data debug

3 files changed, 36 insertions, 3 deletions

diff --git a/examples/albumart.c b/examples/albumart.c
index 51ab400..7fe9077 100644
--- a/examples/albumart.c
+++ b/examples/albumart.c
@@ -34,7 +34,7 @@
 #endif
 
 static void usage(void) {
-  printf("Usage: albumart -i <fileid/trackid> -n <albumname> -s <storage_id> -p <parent_id> <imagefile>\n");
+  printf("Usage: albumart -d -i <fileid/trackid> -n <albumname> -s <storage_id> -p <parent_id> <imagefile>\n");
   exit(0);
 }
 
@@ -58,10 +58,13 @@ int main (int argc, char **argv) {
 
   fprintf(stdout, "libmtp version: " LIBMTP_VERSION_STRING "\n\n");
 
-  while ( (opt = getopt(argc, argv, "hn:i:s:p:")) != -1 ) {
+  while ( (opt = getopt(argc, argv, "dhn:i:s:p:")) != -1 ) {
     switch (opt) {
     case 'h':
       usage();
+    case 'd':
+      LIBMTP_Set_Debug(9);
+      break;
     case 'i':
       idcount++;
       if ((tmp = realloc(ids, sizeof(uint32_t) * (idcount))) == NULL) {
diff --git a/examples/albums.c b/examples/albums.c
index a653126..8296e35 100644
--- a/examples/albums.c
+++ b/examples/albums.c
@@ -34,9 +34,24 @@ static void dump_albuminfo(LIBMTP_album_t *album)
   printf("    Tracks: %d\n\n",album->no_tracks);
 }
 
-int main () {
+int main (int argc, char *argv[]) {
   LIBMTP_mtpdevice_t *device_list, *iter;
 
+  int opt;
+  extern int optind;
+  extern char *optarg;
+
+  while ((opt = getopt(argc, argv, "d")) != -1 ) {
+    switch (opt) {
+    case 'd':
+      LIBMTP_Set_Debug(9);
+      break;
+    }
+  }
+
+  argc -= optind;
+  argv += optind;
+
   LIBMTP_Init();
     
   fprintf(stdout, "libmtp version: " LIBMTP_VERSION_STRING "\n\n");
diff --git a/examples/detect.c b/examples/detect.c
index 393fd2c..8dba1b4 100644
--- a/examples/detect.c
+++ b/examples/detect.c
@@ -64,6 +64,21 @@ int main (int argc, char **argv)
   LIBMTP_error_number_t err;
   int i;
 
+  int opt;
+  extern int optind;
+  extern char *optarg;
+
+  while ((opt = getopt(argc, argv, "d")) != -1 ) {
+    switch (opt) {
+    case 'd':
+      LIBMTP_Set_Debug(9);
+      break;
+    }
+  }
+
+  argc -= optind;
+  argv += optind;
+
   LIBMTP_Init();
 
   fprintf(stdout, "libmtp version: " LIBMTP_VERSION_STRING "\n\n");