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

1 files changed, 15 insertions, 0 deletions

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");