[MERGE] Fix stacking tests applicability

[John Arbash Meinel]

John Arbash Meinel has voted comment.
Status is now: Semi-approved
Comment:
If I understand correctly, the basic change you made is to switch:
         target = source.bzrdir.sprout('target').open_branch()

so that if it raises UnstackableBranchFormat it translates that error 
into "TestNotApplicable". And you did this for several different tests. 
Is that correct?

IMO, that is not the correct fix. Consider the causes:

1) source.bzrdir.sprout('target')

This doesn't seem like something that should *ever* raise 
UnstackableBranchFormat.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3Cm2vdtgb9pa.fsf%40free.fr%3E
Project: Bazaar