typo correction
<TODO> if no obs, return background
empty TimeWindowObs

Modified also TWObsJTerm.
Normally, minimizing should return first guess
obs.plotObs: added observability kwarg
added StaticObs.modelEqNorm()
Added B^{-1/2}, B^{-1/2}^T and B^{-1} operators

Sqrt ops don't pass the adjoint test (~1e-7)
fft_Adj passes.
typo correction: still adjoint test issue for B^{-1/2}
working on B_isoHomo_inv
still looking for B_isoHomo_inv problem
Removed filtering from B ops

With spectral filtering, inverse operators are
ill-defined.
Now the following test works:
  nXi=[]
  for i in xrange(100):
     xi=np.random.normal(size=N)
     nXi=normBinv(B_sqrt_isoHomo_op(xi))
  np.mean(nXi)=N
standard exceptions for precondJTerm.py
added normalized B^{-1} norm
possible error in B^{-1/2}
fixed (patched) B^{-1/2}
xlim for sampling obs
adapted covariance B-1 norm
forcing structure normalization in normBInvAdapted2
minor correction
corrected TimeWindowObs.modelEquivalent
THERE WAS NO ERROR in obs