fixing gnuplot-iostream path and scan=yx usage
removing long double from test_concurrent_1d test as it fails with new gnuplot-iostream
fixing gnuplot-iostream search path in test_mpdata_1d_opt_nug.cpp
making Kahan on by default
adding epsilons to FCT fractions (previously only in iga variants)
optimising the epsilons in FCT - now frac()/where() is not needed at all!
yet one more compatibility fix for newer gnuplot-iostream
Merge pull request #127 from slayoo/master

Kahan on by default; epsilons in all FCT variants; gnuplot-iostream fixes