Reducing branching in sqrt_matrix routine
Only use variances when selecting replacement steps. This breaks
affine invariance, but is much faster, as only N terms need to
be calculated in multivariate normal density function, versus N^2.
This is a major speedup. It still needs work - replace gsl matrices
with double arrays and ditch linear algebra subroutines.
Merge branch 'save-best' into faster-replacement

Conflicts:
	scripts/plotpdf.py
Tweaking burn-in parameters
Strengthening priors on los fit. Increasing use of replacement steps in burn-in.
Tightening los priors and range of guesses
Increasing range of guesses slightly.
Reducing strength of SFD prior.
Set strength of SFD prior to 15%
Adding warning to plotmap.py if file fails to load.
Merge branch 'faster-replacement' into develop