Add possibility to add a model object specific internal precision.
Use default running precison 1.0e-3, which is also the Softsusy default
TOLERANCE
Set the model precision only once, since intenally this precision
is used within run_to()
Use tolerance values which agree with softsusy
Use `precision' in the mass iteration as well.
Make sure the ewsb iteration precision is at least as small as
the running precision
Add test for the calculated running fermion masses at MZ
Test the calculation of the Z mass and the Vev at MZ
Test vevs.  The difference of 2% between Softsusy's and our Yukawa
coupligs comes from the different vevs used in the calculation: In
Softsusy the new vev (= the value of the vev after
sparticleThresholdCorrections() was called) is used to calculate the
Yukawa couplings.  However, we use the old vev (= combination of vu,
vd from the last run) to calculate the Yukawa couplings.