Fix how 'current' branch is determined in updateBitsBranchPointers

updateBitsBranchPointers should determine 'current' by globbing directory names
in /a/common, not /usr/local/apache/common-local, since the new branch is not
there yet when updateBitsBranchPointers is called from checkoutMediaWiki.

Change-Id: I1e6c5a3b8f29a7cfacc30e6bb4220311850580a2