Note to myself: don't fix signs while listening to talks!!
Other mods/fixes:
* 2LPT is now supported also with distinct baryon/DM
power spectra. This creates now an overhead when
using Eisenstein&Hu or BBKS. But who cares.
* Reverted to determinant formulation of LLA rather than
second order expansion. This is much more accurate.
* Added baryon density filter. Baryon density field is now
consistent with CIC DM density. This is achieved by
convolving with an additional grid cell filter (and
no deconvolution).
* Tested LLA, skewness is now exact to a few per cent
but tends to be systematically higher.
* 2LPT needs a bit less memory now in multigrid mode
(FFT based 2LPT still needs humongous amounts).
* Cleaned up code output.
