In the "test-bt" target, replace the call "$(MAKE) test-embedded" by the actions of that target.


Makefile.am:
  In the "test-bt" target, replace the call "$(MAKE) test-embedded" by the actions of that target.
  
  Reason:
  For release builds, we run the tests in a tree that contains just a binary installation.
  So the Makefile is not in the test tree, and we explicitly address it in the build tree.
  This explicit path is not kept by "make", so it is missing in the sub-make.
  There seems to be no way to solve this with (portable!) "make" features -
  we could add a new variable and use it in the sub-make, but it is easier to duplicate these few lines.