2 dirs in exclusiveAccess.dirs cannot run at the same time

[Weijun Wang]

If I have 4 tests

    a/A1, a/A2, b/B1, b/B2

and set

    exclusiveAccess.dirs=a b

all 4 tests must run one by one. Why?

My understanding is each dir in this set has its own "exclusive" 
resource that can only be accessed by one test (inside this dir), but 
different dirs are not related. Therefore although A1 and A2 cannot run 
at the same time, A1 and B1 should.

Thanks
Max