bitbake: Merge further fixes from upstream 1.8 branch

* Make the test functionality work
* Optimise BBPATH handling when changing directory
* Optimise file globing for BBFILES

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/data.py

@@ -553,7 +553,9 @@ def inherits_class(klass, d):
 def _test():
     """Start a doctest run on this module"""
     import doctest
+    import bb
     from bb import data
+    bb.msg.set_debug_level(0)
     doctest.testmod(data)
 
 if __name__ == "__main__":