- cleaned up psd(), now the same as in spydr
- added user mask for SVD eigenvalues (ev_user_mask)
- influence function rotation now correctly rotates actuator
  coordinates too.
- Added option to feed external imat to inversion process (use_user_imat
  and user_imat). Set use_user_imat=1 and put imat to use in variable
  user_imat
Merge branch 'master' of github.com:frigaut/yao