Remove bool arguments to resize

This is the second half of the Uninit changes.  It replaces

  a.resize(n,false)        with             a.resize(n,uninit)
  a.resize(n,false,false)  with  a.clear(); a.resize(n,uninit)

In addition, there are now uninit version of extend and append,
which add newly uninitialized entries to an array.