extensive orb_advert_t fixes

The calls to orb_advertise were being mishandled throughout the code.
There were ::close() calls on memory pointers, there were checks
against < 0 when it is a pointer to a object and values larger than
0x7ffffffff are valid. Some places orb_advert_t variables were
being initialized as 0 other places as -1.

The orb_advert_t type was changed to uintptr_t so the pointer value
would not be wrapped as a negative number. This was causing a failure
on ARM.

Tests for < 0 were changed to == 0 since a null pointer is the valid
representation for error, or uninitialized.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/uORB/uORB.h

@@ -135,7 +135,7 @@ __BEGIN_DECLS
  * a file-descriptor-based handle would not otherwise be in scope for the
  * publisher.
  */
-typedef intptr_t	orb_advert_t;
+typedef uintptr_t	orb_advert_t;
 
 /**
  * Advertise as the publisher of a topic.