iterate to convergence, 32 vs 64 bit

[gary]

the default value for the relative error in the iterate to convergence command was changed from 0.2 to 0.1 in r3102 (conv.autocv in zero.cpp). This was to better predict the outward flux in lines, as per the eigenvector 1 paper. Further, conv_itercheck.cpp checks that the outward flux in Hb changes by less than this value.

with this change several blr sims take quite different numbers of iterations to converge on 32 vs 64 bit systems. This change in the default relative error is being reverted in r3154.

the worst offender was blr_n11_p20 - 5 iterations in 64 bit, 9 in 32 bit